BOOK REVIEW : Seeing Life Through Mud-Colored Glasses : NO CURE FOR CANCER, <i> by Denis Leary</i> , Anchor Books/Doubleday $8; 160 pages

What Denis Leary looks like is better known these days than the way he writes. He is less familiar as an author or comedian than as the skinny guy in the Nike TV ad, confronting the viewer while Bo Jackson exercises to excess in the background.

With his signature line, “I think you hear me knocking and I think I’m coming in,” Leary exudes a certain ill-defined menace. Ill-defined because you don’t really know whether, once this guy comes in, he’s going to steal your VCR, criticize your clothes, drink all your beer or just put his feet up on the cocktail table.

Leaving Dan Quayle jokes to the harmless, risk-free comics (what he calls “disco comedians”), Leary threatens his audiences in order to challenge them. Leary’s father was an immigrant from Killarney who settled in Worcester, Mass., as an auto mechanic.

Leary started doing stand-up as a member of the Comedy Workshop at Boston’s Emerson College in Boston. He took his dark solo comedy routine to New York, where he received this review in the New York Post: “Denis Leary spread eight seconds of material over what seemed like 45 days.”

He fared better at the Edinburgh International Arts Festival, where the show on which this book is based won the Critics Award.

Leary’s show/book contains some very funny, original and valuable material, although many routines probably play better on stage. There is some unfunny stuff that is disturbing: His father beat him; he looks forward to beating his children. The problem here isn’t so much that Leary’s material is risque but that his observations seem ill understood.

Leary speaks for the dissolute generation that wants to shape up, the old-looking early-thirtysomethings. “We snorted and drank and rocked our way through the last 20 years and now--sobered and surprised--we wonder why the problems on the planet haven’t been fixed.” They’ve been too stoned to accomplish much, such as medical research--thus the title “No Cure for Cancer.”

A father himself, Leary confines himself to legal drugs like Nyquil. “It says on the back of the Nyquil box, ‘May cause drowsiness.’ It should say, ‘Don’t make any plans, OK? Kiss your family and friends good-by. . . .’ ”

He also does tobacco and hamburgers and sticks up for the smoking meat-eaters of the world.

“Doesn’t matter how big the warnings are. You could have cigarettes that were called ‘Warnings’; you could have cigarettes that came in a black pack with a skull and crossbones on the front, called ‘Tumors,’ and smokers would be lined up around the block saying, ‘I can’t wait to get my hands on these things, can you? I bet you get a tumor as soon as you light up.’ ”

“I love to smoke so much that I’m considering getting a tracheotomy so I can smoke two cigarettes at the same time.” Leary’s humor builds--or, to put it more darkly--feeds on itself. For example: “I love to smoke and I love to eat red meat and I only eat red meat that comes from cows that smoke.”

Life, through Leary’s mud-colored glasses, seems to be a sort of horrible fun.

“Most people think life sucks, and then you die. Not me. I beg to differ. I think life sucks, then you get cancer, then your dog dies, your wife leaves you, the cancer goes into remission, you get a new dog, you get remarried, you owe $10 million in medical bills but you work hard for 35 years and you pay it back and then--one day--you have a massive stroke, your whole right side is paralyzed, you have to limp along the streets and speak out of the left side of your mouth and drool but you go into rehabilitation and regain the power to walk and the power to talk and then--one day--you step off a curb at Sixty-Seventh Street, and BANG you get hit by a city bus and then you die. Maybe.”

Leary’s not as impish as Lily Tomlin nor as self-absorbed as Spalding Gray.

Unlike Tomlin’s “Search for Intelligent Life in the Universe” or Gray’s “Swimming to Cambodia,” “No Cure for Cancer” is more than a comedy routine but still less than a book. It’s stand-up: good, original stand-up from an undeniably talented guy.

You could give this as a Christmas gift to someone. And the message of this gift would be, “You’re tough; you can take it.”