WHEN YOU STOP and think about it - and if the American Film Institute's gargantuan ninetysix-film "Love Stories" series running through September 1 at the Kennedy Center does nothing else, it certainly makes you stop and think about it - almost every film ever made could be called a love story.

Isn't "King Kong" merely a cautionary tale of unrequited love, of beauty toppling the beast? Didn't "Harry and Tonto" show that a man and his cat could have a perfectly adult relationship? Don't Butch and Sundance care about each other as much as Bogart and Bacall ever did? And what about those debilitating "love interest" segments in otherwise anarchie Marx Brothers outings? Whoever wrote "Love is all around" must have spent a lot of time at the movies.

It's always been that way, even way back in 1896, when one of the first pieces of film to cause a sensation was what else but "The Kiss," a horrifying (to some) close-up of lips entwined in osculatory bliss. How romantic!

It would probably take Aristotle to fully explain the reason love and the movies get on so well together. It has, no doubt, to do with being in the dark, with being able to watch wonderful-looking people do and say things you'd never quite have the nerve to attempt youself, always having the sure knowledge that everything they did would turn out all right. Maybe not happily ever after, I didn't say that, but all right satisfying, in the way that is really the ultimate separating point between romance in life and romance in the movies.

As long as films have had stars, the best and the brightest of them have been romantic ones. While some can be locked into a specific time slot - like Jean Harlow of the early Thirties, always cracking wise, or Theda Bara (real name Theodosia Goodman), a tailor's daugher fromCincinnati who put kohl under her eyes and vamped every man in sight just after The Great War - the best of the romantic stars, like Garbo or Cary Grant, are genuinely timeless, as vivid now as anyone could wish.

Maybe they're even more vivid now, because one of the things Hollywood seems to have lost along with its vaunted innocence is the ability to make simple love stories. So whenever anything at all in that general area comes along - the French Allen's "Annie Hall" this year - an apparently affection-starved audience responds by simply going amuck at the box office.

People do tend to be fanatical about their favorite film loves, so even though the AFI series is the beggest theme event the theater has ever run, even though the primarily American selection of films is dizzying in its eclecticism, much that everyone knows should have been included is missing.

No films directed by Truffaut or Lubitach and no films starring Katherine Hepburn or Greta Garbo are included because the AFI is planning full tributes to them later on. "Elvira Madigan" and "Love Story" are missing because they are too obvious, Hedy Lamarr's pseudo-racy "Ecstasy" because it was too hard to get, a 1961 American version of "Fanny" is being shown because the classic French "Marius"/"Fanny"/"Cesar" trilogy is out of circulation, and "Children of Paradise," probably the greatest romantic film ever made, is gone because it just played an extended run at the Key. Such is life.

Not that there is any lack of films to choose from, everything from silents like the 1922 "Salome" starring the fabled Nazimova to rowdy musicals like "Seven Brides for Seven Brothers" and "Kiss Me Kate." (Sorry folks, no 3-D this time.)

With almost every director anyone ever heard of having tried his hand at a love story at one time or another, the AFI has provided quite a selection, from obvious romantics like Vincente Minelli directing wife Judy Garland in "The Clock" to more unusual picks - John Ford and "The Quiet Man" - and ending with heavier types still, like Alain Resnais ("Hiroshima Mon Amour") and Antonioni ("L'Avventura"). Ingmar Bergman is represented by the funniest, most carefree film he ever made, "Smiles of a Summer Night" (it almost seems like a mistake), and Bernardo Bertolocci, not by "last Tango," a romance of sorts, but "Before The Revolution," his first feature, made at the precocious age of 25.

And when it comes to the heart-throbs, the stars who launched a thousand handkerchiefs and made it all worthwhile, the selection is wider still, starting with Valentino in the torrid (sort of) "Son of the Sheik" and Dietrich turning men to putty in "The Blue Angel," and going all the way to Julie Christie in "Darling" and the heart-breaking Laura Antonelli in "Malizia."

Men, eat your hearts out over exotic Ava Gardner in "Mogambo" and "Bhowani Junction," or Grace Kelly, the original ice princess, in "High Society," her final film. Women, sigh endless sighs over a criminally young Laurence Olievier in "Wuthering Heights," over Marlon Brando as a brooding Napoleon in "Desiree," over the swashbuckling antics of scamps like Tyrone Power ("Blood and Sand") and the adventurous Errol Flynn, as in "The Adventures of Don Juan" and "The Adventures of Robin Hood."

For those who just after statistics, the star who shows up most in this series is local resident Elizabeth Taylor. Her seven appearances go from the 1948 "A Date With Judy" to a 1960s Richard Burton trilogy of "Cleopatra," "Who's Afraid of Virginia Woolf?" and "The Taming of the Shrew." oddly enough, Taylor's most luminous role, practically searing the screen with carnality as wealthy debutante Angela Vickers in "A Place In The Sun," is not in the Love Stories series but can be seen at the AFI on August 7 as part of a tribute to co-star Montgomery Clift.

Despite the great size of this series, there are half-a-dozen films that stick out above the rest. These are acknowledged classics of romantic filmmaking, films peated visits but rather give the viewer more each time he sees them. Three are American, three are French, some familiar, others not, but none should be missed, no matter how often you've seen them:

"Casablanca" - Bogart, Bergman and a lot of piano playing somehow coalesce into a film that lives up to all that has been written about it, which is plenty.

"Casque d'Or" - The title refers to the golden hair of a young Simone Signoret who many critics, including Francois Truffaut, think has never been better than in this oh-so-fatalistic romance set in the turn-of-the-century Paris underworld. Little seen, but guaranteed to please.

"Cesar and Rosalie" - The most modern of the six, filmed in splendid color, starring Yves Montand in a wonderfully bittersweet romantic triangle that shows that the French, at least, haven't lost that loving feeling.

"The Earrings of Madame De . . ." - Not only one of the classic romantic films, this Max Ophuls extravaganza, set in Vienna and fairly dripping with elegance and weltschmertz, has devotees who think it is among the two or three best films ever made, period. Money back guaranteed to anyone who isn't reduced to a mass of sniffles.

"East of Eden" - The only one of James Dean's three movies that hasnt dated and continues to justify his post-humous reputation. Based on the Steinbeck novel and graced with excellent costars like Julie Harris, Jo Van Fleet and especially Raymond Massey as the father figure to end all father figures. Arguably not really a love story, but who wants to argue?

"A Streetcar named Desire" - Marlon Brando has never done anything better on film, but for that matter neither has any other American actor, than this portrayal of Stanley Kowalski, a man with more than a passing interest in the napoleonic Code. The film won five Oscars, including acting awards to Vivien Leigh, Kim Hunter and Karl malden, but Brando lost out to Bogart in "The African Queen."

While most of these films have more than a smidgen of heartache in them, they have nothing on a trio of fiercely ill-fated romances, classics in a minor key, that act like the happy ending was all a terrible mistake:

"Double Indemnity" - Fred MacMurray is a long way from Walt Disney as an insurance agent seduced by Barbara Stanwyck, the ultimate film noir heroine, into bumping off her husband to collect a big insurance bonus. They figure all the angles except Edward G. Robinson, a claims investigator who never sleeps. Said one critic, "A film without a single trace of pity or love." Another film noir romance worth seeing is "Gun Crazy," an early variation of the "Bonnie and Clyde" theme.

"The Dybbuk" - This extremely rare, Yiddish-language film made in Poland just before the Nazi takeover has a haunting quality that is extraordinary. A singular tale of broken promises, supernatural possession and love beyond the grave.

"Lolita" - Stanley Kubrick directed, Nabokov wrote the screenplay from his novel, and Sue Lyon made it very easy to understand the heavy-breathing rivalry of James Mason and Peter Sellers, rivals in lust if not exactly in love. Not as shocking after fifteen years, but still quite audacious.

After all this angst, it seems only right to be reminded that not all film romances ended in tragic agony, that the making of light comedies where everyone ended up happy no matter how enormous the obstacles - and those obstacles could be pretty enormous - was once a movie staple. Most people are familiar with good-humored examples like "It Happened One Night," the alleged death knell of the American undershirt industry, or "How To Marry A Millionaire," with Marilyn Monroe as a girl who can't tell men apart because she's too vain to wear glasses. But other, less well known films are as diverting, if not more so. For instance:

"The Lady Eve" and "The Palm Beach Story" - Though you hear precious little about him today, in the early 1940s writer-director Preston Sturges made the wittiest, most cynical sexcomedies Hollywood has ever seen, before or since. These two films are his best, and their panache and hilarity never fail to amaze modern audiences, however jaded they may think they are.

"Love Me Tonight" - Maurice Chevalier does what only Maurice Chevalier can do, whatever that is, as a tailor who is passed off as a baron in this charming musical comedy that some folks even consider enchanting.

Pride and Prejudice" - Pleasingly faithful to the spirit of the Austen novel, courtesy of a screenplay coauthored by Aldous Huxley, this is an engaging comedy of manners with a well-matched team of Laurence Olivier and Greer Garson that is absolutely just right.

Not quite as much fun, at least not on purpose, are those movies which fall under the category of weepies, formerly known as "women's pictures," three-hanky pictures, etc: Though not for scornful types, all others will find it terribly easy to sob along with the multitudes. The pick of the lot look to be "Waterloo Bridge," with Vivien Leigh and Robert Taylor; "Seventh Heaven," the premier silent weepie; "Make Way For Tomorrow," a heartbreaker about senior citizens, and "Written On The Wind," starring Rock Hudson and directed by the master of the art, Douglas Sirk.

And, of course, this wouldn't be an AFI series if it didn't have its share of, shall we say, unusual films, oddities which have found their way into the program under one guise or another.

Among these "You'll Never See This One Anywhere Else" films are "Three Comrades," the only screen-play for which F. Scott Fitzgerald received screen credit; "Under Capricorn," probably Alfred Hitchcock's biggest financial disaster, "The Mother and The Whore," a largely unwatchable three-and-a-half hour piece of French torture; the long-unseen 1949 Alan Ladd version of "The Great Gatsby"; a "college jocks in love" double bill of "Tall Story" and "Good News"; the first F.W. Murnau double bill in human memory ("Tabu" and "City Girl," if you're interested); "The Garden of Allah," famous for its Technicolor brilliance and nothing else; and a pair of films featuring what programmer Mike Clark calls "two couples who will probably never appear in Penthouse: 'Tarzan, The Ape Man' and 'The Bride of Frankenstein.'"

And they say that falling in love is wonderful.