VIDEO . . . WHAT’S NEW : If You Haven’t Seen It, Rent ‘Batman’ Before Buying : THIS WEEK’S MOVIES

This has been designated Home Video Week by the Video Software Dealers Assn., but for millions of eager fans it’s simply Bat-week.

Two days ago, Warner Home Video released “Batman,” the blockbuster fantasy that opened in theaters only five months ago and set box-office records.

Despite all the hype over the PG-13-rated movie, which stars Michael Keaton as Batman and Jack Nicholson as the Joker, despite the fact that it was directed by the talented Tim Burton (“Beetlejuice”), and despite the low price--$24.98--you may be better off renting the tape for a $2 preview before you buy. Unless, of course, you’ve already seen the movie and know you want to spend $25 for it.

Why?

Over the next few weeks, “Batman” may break the video-cassette-sales records set by “E.T.” (the laserdisc won’t be out until early ‘90), but unlike “E.T.,” this was not a movie that was (nearly) universally loved. Lost amid all the Batmania is the fact that the film disappointed many people.

Times film critic Sheila Benson, for example, wrote that only Keaton’s performance “keeps the picture alive; it’s certainly not the special effects, the editing, which has no discernifble rhythm, or the flaccid screenplay.”

And in the newly released 20th-anniversary edition of Leonard Maltin’s TV Movies and Video Guide, Maltin gives “Batman” only a mediocre 2 1/2-star rating--a mere half-star more than the 1966 version starring Adam West! “There’s razzle-dazzle to spare in this dark, intense variation on Bob Kane’s comic book creation,” says Maltin, generally a fan of fantasy films and an expert on cartoons, “but there’s also something askew when the villain is so much more potent than the hero!”

Of course, there were several critics--and millions of filmgoers--who loved the movie. However, there’s one more thing you’d better not expect from this ballyhooed “Batman”--Robin.

Other new-on-tape movies:

“The Adventures of Baron Munchausen” (RCA/Columbia, $89.95, PG) might please a lot of “Batman” fans. Also a big-budget fantasy that was preceded by another version (two, in fact, in 1943 and 1961), “Munchausen” is a special-effects-and-fun-filled movie about an 18th-Century traveler. It’s another far-out film from Terry Gilliam, who did the crazy artwork for Monty Python and made the brilliant “Brazil.”

“The Wicked Stepmother” (MGM/UA, $79.95, PG-13) is another 1989 fantasy / comedy, but one that will be remembered only as the unfortunate final project of the great actress Bette Davis--she left the movie during production and the script was rewritten accordingly, and disastrously.

“K-9” (MCA, $89.95, PG-13) is the first and worst (by a sniffing nose) of 1989’s dog-and-man-detective-team films to be released on video (still to come: “Turner and Hooch”). Jim Belushi plays a narcotics officer who works with a headstrong German shepherd.

“The Rainbow” (Vestron, $89.98, R) returns director Ken Russell and star Glenda Jackson to D. H. Lawrence territory, with far less pleasing results than the film that made both famous, “Women in Love” (1970, available on video).

“The Dressmaker” (Capitol, $79.95, no MPAA rating) stars the great veteran British actresses Joan Plowright and Billie Whitelaw in a low-budget, low-key film that starts off nicely and then goes awry. It’s about two very different Liverpool sisters whose niece falls for an American soldier during World War II.

Four oldies from MGM/UA ($19.95 each):

“Yours, Mine and Ours” (1968) isn’t the best comedy ever made by its stars (Lucille Ball and Henry Fonda, who, incidentally used to date back in the pre-Desi days), but it’s a fine family film--in more ways than one. Ball plays a widow with eight children who marries a widower (Fonda) with 10 of his own.

“A Hole in the Head” (1959) unites two great Franks (star Sinatra, director Capra) with disappointing results--it’s a gooey son-and-dad drama--but among the occasional pleasures is the delightful song “High Hopes.”

“The Wonderful World of the Brothers Grimm” (1962) has a few colorful, playful renditions of Grimm fairy tales, but the framing story of the tale-collecting brothers (Laurence Harvey, Karl Boehm) is a drag.