Suited to a T : Don’t want to wear your heart on your sleeve? Since the humble T-shirt evolved from underwear to mass medium, you can wear your thoughts on your chest.

If California is the laboratory for American pop culture, it’s also the dressing room--at least when it comes to that most generic of garments, the ubiquitous T-shirt.

A fictional Hollywood producer sported the first T-shirt immortalized in print--the Oxford English Dictionary pins that honorable mention on F. Scott Fitzgerald’s 1920 “This Side of Paradise.”

It took one movie star to persuade American men to doff their T-shirts--when Clark Gable bared his chest in “It Happened One Night” in 1934, sales dove. It took another to inspire men to don them--Marlon Brando’s sensual Stanley Kowalski in 1951’s “A Streetcar Named Desire” made the humble T the epitome of sartorial machismo.

And when Ed Roth, the Big Daddy of California’s car culture, aimed his hot-rod-customizing airbrush at T-shirts in the early ‘60s, he helped steer their evolution into wearable canvases that broadcast the bearer’s take on life.

“It identifies the tribe you belong to,” says Richard Martin, curator of the Metropolitan Museum of Art Costume Institute in New York. “There’s something about the identifying, speaking T-shirts that is very powerful in terms of a sense of the moment and in the moment, finding one’s place in society.”

Indeed, the T-shirt’s role as a walking billboard--the wearer provides the feet--is taken so seriously as a forum for free speech that it has been deemed worthy of Supreme Court protection.

But not everywhere. In one of the more bizarre stories coming out of the Persian Gulf War, Kuwait sentenced a man to prison for 15 years simply for wearing a T-shirt with Saddam Hussein’s picture.

Even in the United States, wearing the wrong T-shirt can be risky business. A Florida short-order cook was jailed for 10 days two years ago for “coming to court with a T-shirt that says, ‘Haulin’ Ass’ with four naked butts on it,” in the words of the unamused judge who held him in contempt.

Talk about fashion clout. With punch like that, it’s not surprising that the simple T is big business and getting bigger. The American T-shirt industry grinds out $1.7 billion worth of duds a year, filling out our typical wardrobes of 25 shirts a person.

And in tough times like these, the T is particularly appealing. “It’s something inexpensive that people can buy, and it makes them feel good but it doesn’t break them,” says Barbara Montgomery, executive editor of the Dallas-based Impressions, a trade publication aimed at the imprinted sportswear industry. “Their guilt is relieved about making a nonessential purchase, yet it is a piece of clothing. It’s a nonessential essential.”

It’s also outerwear that began life as underwear and its origins have virtually taken on the cloak of legend. One version credits the British monarchy with ordering sailors to sew sleeves on their undershirts to spare royalty the unseemly experience of witnessing an armada of armpits. Ergo, the shirt shaped like the letter T.

Another nautical explanation traces the first Ts to 17th-Century longshoremen who unloaded tea in Annapolis, Md. Ergo, tea became T .

By the early 1930s, the T as we know it was coming out of the closet. Some sports shops were selling shirts with university insignia. And as early as 1939, they were being used to promote a product. In fact, “The Wizard of Oz” spun off its own shirt.

World War II propelled the T into an outerwear basic, the uniform for the modern era. Each military branch ordered up millions in its own color. Some soldiers who fondly remembered their university shirts took to stenciling the names of their camps on Ts. Military men could flaunt their esprit de corps and nothing more on their chests, especially in the toasty tropics.

The T leaped from the Pacific theater to the New York stage in 1949, on the backs of high-stepping sailors in “South Pacific.”

“The T-shirt became heroic in everything from ‘South Pacific’ to the military ideal,” says curator Martin.

Two years after Nellie Forbush tore up the stage in her T, the shirt returned to hug Brando’s biceps in “Streetcar.” The actor’s architecture gave the garment a sexual je ne sais quoi from which America has never recovered. Elvis Presley cheered it on, sneering in a T-shirt and leather jacket. And James Dean perpetuated the Attitude-With-a-T look in “Rebel Without a Cause” in 1955.

By then, the T had already “gone high fashion . . . appearing on city streets and country-club porches--and even at formal dances,” according to the gee-whiz prose of Life magazine.

And as the quintessential American garment, the walking billboard was already taking ads--variously touting the pleasures of beer, natch, and Davy Crockett, in possibly the first TV T. A shirt ballyhooing the erstwhile New York Herald Tribune became such an icon of American culture in late ‘50s Paris that Jean-Luc Godard garbed Jean Seberg in one in the 1959 film “Breathless.”

Back in California, hot-rod culture was heating up, and car customizers like Von Dutch and Ed (Big Daddy) Roth began customizing shirts at the request of fellow hot rodders. Roth drew his first shirt in 1959 for a Los Angeles car club called the Buccaneers of Maywood. From there it was a quick hop to his signature bulging eyeballs, which eventually had his famous Rat Fink character wrapped around them, on everything from Ts to decals.

“When I started drawing the big eyeballs, the kids wanted that more because it made their parents angry,” Roth says. “So the bulging eyeballs came from the parents’ desire not to have that.”

By the ‘60s, unisex Ts were helping flower children bare their ban-the-bombing souls. It was de rigueur for student radicals, who were turning the political T into a uniform for the masses for the first time. The roots of political wear go way back to 1948, when New York Gov. Thomas E. Dewey’s run for President inspired child-size shirts that read: “Dew-It With Dewey,” one of which is housed in the Smithsonian’s National Museum of American History.

But the trend toward outspoken shirts has taken a violent turn in recent years. In some youth circles, it’s fashionable to sport one’s hostility in gang-inspired Ts that wield pictures of smoking guns or convey simply crude or sexist messages.

A Washington, D.C., manufacturer of 9-millimeter-gun shirts was so rattled last year by a torrent of angry calls after his harrowing quote in the local press--”Unfortunately, violence sells”--that he vowed to destroy the offending shirts.

And Fairfax High School Principal Michael O’Sullivan recently saw a hulking student walking down the hall in a shirt blaring a four-letter word.

“I was so stunned by this that my first thought was, ‘Did your mother see that?’ ” says O’Sullivan, who told the student to turn the shirt inside out. “They think (crude shirts) are cool. They think they’re redefining their independence and their freedom from adult constricts.”

Such ‘90s in-your-face assaults on taste recall a tart remark from Fran Lebowitz’s 1978 satirical book, “Metropolitan Life”: “Clothes with pictures and/or writing . . . are an unpleasant indication of the general state of things. . . . If people don’t want to listen to you, what makes you think they want to hear from your sweater?”

Nonetheless, the Supreme Court says your shirt has the right of free speech (within bounds of obscenity laws and school rules). Last year, the court ruled that the First Amendment protects nonprofit groups who sell merchandise with a political, religious or philosophical message.

And such sentiments can be the height of fashion. Cross Colours, a 3-year-old Los Angeles company, quickly made a reputation (and a fortune) marketing Ts with peaceful slogans aimed at deprogramming some of the negative message-bearers. One of its bestsellers simply reads: “Love Sees No Color.”

“We felt that via T-shirt messages was the best way to express ourselves to the person buying the T-shirt,” says company president Carl Jones. “And at the same time, it’s kind of a billboarding effect--when a person wears a T-shirt, other people read it. It became very, very successful for us.”

Such broad exposure was obviously quite tempting to commercial America. Opportunity dovetailed nicely with the rise of the Me Generation in the ‘70s, which found in Ts an outer outlet for its navel-gazing. The T-shirt business exploded, spinning off such curious cultural phenomena as the facetious “My Parents Went to Florida and All I Got Was This Lousy Shirt” shirts.

With many commercial Ts, wearers borrowed the eclat of their heroes, typically in entertainment or fashion. The ‘70s saw the rise of classics commemorating the ephemeral reigns of the movie “Jaws” and actress Farrah Fawcett, whose toothy smile beamed out reportedly from millions of breathless chests.

Rock Ts have become humongous business for performers, who typically take home roughly 40% of shirt-sale proceeds at their concerts. T-shirt sales alone for Michael Jackson’s 1988 tour, for example, amounted to an estimated $12 million. Rock T purchases are also often seen as an early-warning system of a band’s success. Sales of Metallica shirts skyrocketed as the band was taking off several years ago.

“It was very indicative of the hard-core potential the band had,” says Metallica manager Peter Mensch. “People were wearing handmade Metallica shirts because they were cool. It showed people you were into a band that was on the edge.”

The cutting-edge T torch has passed to up-and-coming metal-rappers Rage Against the Machine, which is also enjoying a wave of possibly portentous shirt sales among fans in the know. Such buyable cachet has helped boost sales of “promotional wearables,” as the industry calls them, to $5.22 billion, according to the Specialty Advertising Assn. International.

Huge sales potential has enticed scores of scam artists to market counterfeit shirts. When “Batman” became one of the biggest movie merchandising bonanzas in 1989, it not only engendered millions of dollars in shirt sales but also awakened a swarm of bootleggers.

Warner Bros. dispatched a network of private investigators to ferret out counterfeit merchandise in flea markets and stores in the United States and Canada. With that evidence the company filed lawsuits against “thousands of people in connection with Batman alone,” says Nils Montan, vice president and senior intellectual property attorney for the company.

And when “Batman Returns” came out in 1992, the company identified its licensed merchandise with new hologram hang tags. “(Bootlegging) is a serious problem, but it would be an extra expensive step to start counterfeiting holograms,” Montan says. “If you have a popular item, you can’t stop it 100%. It’s just too easy to silk-screen T-shirts and get them to street vendors everywhere.”

Interestingly, Chanel Ts--made for only one season six years ago--have been so massively bootlegged that fakes are widely mistaken for the real thing.

“We definitely fight it,” says Chanel spokeswoman Arlette Thebault.

While couture is ripped off as a matter of course, the fashion food chain also works in reverse. In an unusual case, British designers Antoni and Alison sued Giorgio Armani last winter for allegedly stealing a T-shirt design.

They claimed their shirt was copied after worldwide exposure, in part because singer Neneh Cherry wore it on her promotional rounds. It read: “I feel amazing, fantastic, incredible, brilliant, fabulous, great.” They said the contested Armani T had similar lettering: “I feel outrageous, amazing, brilliant, terrific, great.” An Armani spokesman declined to comment on the suit.

Tomorrow could bring such hi-tech Ts as 3-D shirts and color-changing duds, using a chemical process called thermocromatics. But for the moment, the T-shirt is coming full circle to the unadorned shirt that was popular in the Fonzie ‘50s.

“It’s the influence of the Gap,” says the Metropolitan’s Martin. “It’s almost what the Amish would wear.”

Indeed, the simple T could be the defining garment of the complex ‘90s. “People are dressing a lot more casually than they used to,” says Price Deratzian, an L.A. designer who recently launched her own line of retro Ts under the label Body Furniture. “And you can wear a T-shirt and still be very, very stylish.”