THINK ABOUT SOVIET cinema long enough and a sigh escapes. A long, heartfelt Slavic sigh, full of teary regret for what might have been, for squandered exuberance and atrophied potential. Because no film industry has ever fallen so rapidly from such a pinnacle, and made such a thud. Such a terrible, terrible waste.

Yet if the AFI's "Soviet Cinema, Yesterday and Today," opening tonight at the Kennedy Center, inevitably calls up those sighs, it provides a bit of an antidote as well. Slowly, painstakinglu, Russian films are coming back. They're not at the top, but they're trying. And after what has come before, even that is something.

The beginnings, of course, were probably the most spetacular in film history. Between 1925 and 1930 the Soviet cinema was prodigal with inventiveness and zest, the envy of the rest of the movie world. "Of all the arts," Lenin had said, "the cinema is most important to us," and with that kind of backing, Pual Rotha wrote in his "This Film Till Now," "the cinematic technique of Soviet directors has developed to a state of efficiency equalled by no other film-producing country in the world."

And it was not a monolithic output, either. A director such as Abram Room could make a droll social comedy about overcrowded apartments titled "Bed and Sofa" at the same tme Alexander Dovzhenko, a romantic dreamer here represented by his 1932 "Ivan," was coming up with poetic evocations of the Ukraine where practically every leaf, every tree filmed had a special meaning to the folks watching back home.

Most strident of the new Soviet directors was Dziga Vertov, a polemicist credited with pioneering cinema verite who believed that "the only true function of film was to bring the facts of the new society to the people who were helping to build it" and who served as the unfortunate inspiration for many of Godard's difficult later works.

As seen in his "Three Songs of Lenin," Vertov himself was anything but hard to follow. Politically naive, yes; worshipful of Lenin to an embarrassing degree, yes - a bench where the Great Man sat is photographed with a reverence usually reserved for pieces of the True Cross - but wonderfully dynamic and spirited nevertheless. Even today. 40 years after the fact, one can share the cork-popping excitement these filmmakers felt at doing work that was technically superb, and which they were sure would change the world.

Unfortunately it was they, not the world, who got changed, and there is no better example of how than Sergei Eisenstein's "October," which opens the AFI series at 9 tonight.

Conceded to be the best of the Soveit directors, a master of montage technique who was blessed with a sweeping sense of history, Eisenstein had problems right from the start in filming this story of the Revolution adapted from "Ten Days That Shook the World" by American socialist John Reed. For one thing, the Winter Palace apparently suffered more damage during the recreation of the Revolution by drunken veterans than it had during the actual event.

But this was nothing compared to what happened when "October" was ready to be released. Stalin and Trotsky had just had their famous falling out and the latter, perhaps the key figure in the struggle had to be totally eliminated from the film, skewering it terribly from a historicl point of view and causing a one-year delay in its screening.

More than that, Eisenstein faced for the first time charges of "formalism" from the party bureaucracy, charges that he was getting involved with bourgeois esthetic considerations at the expense of enlightening the masses. Though he continued to make films, and excellent ones, a well-founded sense of being hounded stayed with him right up to his premature death.

The simultaneous arrival of both sound and Stalin began a quarter-century of almost complete somnolence for what used to be the liveliest of film industries. This was the notorious era of "socialist realism," of stilted boy-meets-tractor romances, a period the AFI avoids for obvious reasons, though perhaps showing one of those sturday bores might be interesting for historical reasons.

The first signs of a post-Stalin thaw came in the late 1950s, but the films produced then - "The Crane Are Flying" is a good example - tended to be overwhelmingly sentimental, as if no one in the whole country had been allowed to cry until now, but had saved their tears in anticipation.

Much more interesting, and where the brunt of the AFI's films can be placed, is in Soviet production since 1970. Good as they are - and some are quite good - they must be recommended with an important caveat. By and large they are interesting not so much in themselves but as examples of what the Soviet authorities, sensitive as are no others about admitting even the tiniest of shortcomings, are letting both their own people and the rest of the world see on the screen.

This is the case for instance with "Ascent," the winner of the Golden Bear at this year's Berlin Film Festival, a film that is especially notable for its quasi-sympathetic outlook toward a World War II collaborator as well as the striking Christian symbolism of its ending.

Other films, like "Dersu Uzala," a Japanese-Soviet coproduction directed by Akira Kurosawa, and two items from Soviet Georgia, "Prisomani," the muted story of a famous primitive artist, and "The Invocation," a dazzling epic myth, are notable primarily for their visual content and make no overt comment one way or another about Soviet society.

The most interesting AFI showings, however, strike a distinctly new tack. They allow privileged looks into everyday Soviet life, do not shy away from inadequacies and compromise, and even boast moments of a kind of "Our Town" charm while providing an outsider with the best picture he is likely to get of ordinary Russians being hearteningly ordinary.

"May I Have the Floor," for instance, focuses on the female mayor of a medium -sized Russian city and her attempts to deal with nonidealists ranging from her children - who are interested only in material goods and the Beatles, not necessarily in that order - to her predecessor, intent on a new sports stadium, who tells her "Mayors come and go, but football's here to stay." Now doesn't that sound familiar?

While "May I Have the Floor" is a serious film with moments of great warmth and feeling, "Afonia" is an out-and-out comedy about a loveable rascal of a plumber who is always turning up on the "Shame the Drunks" Board. Hard as it may be to imagine, this is a light, frothy affair with all the charm of a similar effort from France or Italy, as well as being quite candid, for a Soviet film, about society's weaknesses.

Not that everything is getting out. "Andrei Roubley," a highly regarded historical epic by Andrei Tarkovsky, director of "Solaris" and perhaps the best of current Soviet directors, is finally getting to Washington eight years after it was made; but no luck with his latest and most controversial film, a many-levels-of-reality work called "The Mirror."

While it may seem strange that anything like this could even get made in the Soviet Union, there is apparently a Russian word that covers it: "pokazuka." Pokazuka roughly refers to something made for show, a film that the authorities had no intention of ever widely distributing but allowed to be created just so they could say "Look at the kind of adventurous films we're producing."

Maybe next year.

The schedule: