Until recently, movie soundtracks were relegated to a far corner of the record bins, black sheep among the million-sellers. No one paid much attention to them since film music was widely considered background, used primarily for credits and to signal some important scene in the movie. No more.

"A Star Is Born" was a chart-topper (even at a then-outrageous $8.99) and "Saturday Night Fever" broke all kinds of sales records. Though that album's success could be rationalized as a triumph for the Bee Gees rather than the silver screen, no one could deny that the Top Five status of "Star Wars" was based on the appeal of the soundtrack. Since then, "Grease" has become what the biz likes to call "a monster," and other film scores have enjoyed marked commercial success.

So if you're planning to go to the movies this weekend, you might be able to use a guide to the music that goes with them. You never know when you might be watching America's next big album.

SUPERMAN -- Big promotion, big orchestra, big composer, big bucks. Everyone connected with "Superman" fully expects this two-record set to be the next "Star Wars," and the expansive (and expensive) publicity is constantly adding fuel to its own fire. Actually, ther score sounds a lot like the original "Star Wars," though a bit less celestial. The music is zestfully played by the London Symphony Orchestra conducted by composer John Williams, the man responsible for both "Star Wars" and "Close Encounters of the Third Kind." And a man who now uses Oscars for bookends. This album is much like its movie -- a lot of fun if you don't take it too seriously. Also, it's almost sure to be nominated for an Academy Award since it's difficult to slight a record that stands for truth, justice and the American Way.

MOMENT BY MOMENT -- Once you stop chuckling at the front jacket, which pictures John Travolta and Lily Tomlin as a set of identical twins, you'll find that there's some good stuff on the disc. This soundtrack is from the school that believes that any snippets of music heard in the film qualify for the soundtrack. Since the movie has a lot of scenes of people driving in cars with their radios on, we get Michael Franks' "The Lady Wants to Know," Stephen Bishop's "Everybody Needs Love," Dan Hill's maudlin smash "Sometimes When We Touch," 10CC's "For You and I," and two Charles Lloyd compositions. We also get five different versions of the title track. Still, John Klemmer's sax solos save two of them and Yvonne Elliman's sentimentality is just right for two others.

ANIMAL HOUSE -- This is not a great record, but John Belushi is big box-office right now and here we have him leading the troops through a rousing "Louie Louie." The ever-present Stephen Bishop contributes the title cut and "Dream Girl," and there's a welcome dose of nostalgia from Sam Cooke's original "Twistin' the Night Away." Elmer Bernstein's score will do, but the movie's better.

THE LORD OF THE RINGS -- This one screams "epic !," but it tends to drag. Composer and conductor Leonard Rosenman has experience with similar heavies ("Barry Lyndon," "Bound for Glory"), and the score does project images of fantasy. But not enough of this double album is left to the imagination. And that's what the Tolkien trilogy was all about.

EVERY WHICH WAY BUT LOOSE -- Clint Eastwood doesn't sing, nor does his orangutang co-star. Many of the vocalists here are bona fide country-music stars (Eddie Rabbitt, Charlie Rich, Mel Tillis) and album producer Snuff Garrett is a seasoned vet. Rabbitt's title tune is catchy and Cliff Crofford comes up with a playful "Monkey See, Monkey Do" (not to be confused with Michael Franks' song of the same name). The album has the required instrumental filler, but generally it's a pleasant piece of country pop.

WATERSHIP DOWN -- This one starts out like "Peter and the WOLF," COMPLETE WITH A PROLOGUE SPOKEN OVER A RAGING INTRODUCTORY THEME. The classical music that follows is more interesting than the pieces on "The Lord of the Rings" primarily because, though the film's subject matter is heavier, "Watership Down" has music that's lighter. Art Garfunkel sings "Bright Eyes" with sensitivity oozing from his adenoids, and Amgela Morley's compositions stand up for most of the album. Not a bad release for a bunch of rabbits.

CALIFORNIA SUITE -- You might expect a Neil Simon film to be much more interested in laughs than music, but this soundtrack could be the best of the bunch. For one thing, it features authentic jazz players: Hubert Laws, Chuck Domanico, Claude Bolling, Shelly Manne, Bud Shank, Tommy Tedesco and Ralph Grierson. For another, the tunes do not need the film to support them. The title theme swings and both Bolling's piano and Laws' flute keep the tempo moving. Some of the slower pieces are pretty, if less imaginative, and none of the compositions will send you running from the room. Or suite.

MIDNIGHT EXPRESS -- Composer Giorgio Moroder tries to capitalize on the hypnotic effects of electronic music, and it works for a while. Hes theme is suitably unnerving and has a pseudo-disco beat to boot. However, despite some varied interludes, the album often sounds like your needle's stuck somewhere in the middle of the main title. Electronic music often suffers from repetition, and "Midnight Express" is no exception. It says on the jacket that 43 days after the world press saw this film at Cannes, the United States and Turkey began prisonerexchange negotiations. If the world press heard the album, 43 days later they'd have forgotten all but a few bars.