"In the Realm of the Senses," now at the K-B Cerberus 1 and 2 and K-B Janus 1, was the hottest attraction at the 1976 Cannes Film Festival. The first screening evidently caused such a mob scene that a dozen subsequent screenings were required to appease the demand.

One can't help wondering if the people clamoring to get in felt quite so enthusiastic on the way out. There's no denying that Nagisa Oshima, the writer-director of "Realm," takes his morbidly erotic subject matter seriously, and it would be fair to regard this picture as the first legitimate successor to Bernardo Bertolicci's "Last Tango in Paris." The people who felt "Tango" was copping out by stopping at stimulated sex acts may even consider "Realm" more honest and audicious because its leads have been required to go beyond simulations.

However, Oshima's tone is no less solemn than Bertolucci's, so the hardcore interludes in "Realm" are never calculated to arouse prurient interest. The movie might be more entertaining if they were. It would certainly be less oppressive if Oshima perceived his story about a fatally overpowering sexual passion as something less portentous than grand romantic tragedy.

The scenario was inspired by a murder case that supposedly electrified Japan in 1936. A young woman named Sada Abe was discovered in a daze on the streets of Tokyo clutching the severed genitals of her late lover. As the events were reconstructed, it appeared that Sada had gotten carried away after an extended sexual liaison and calminated the affair by abstracting her beloved's sex organs.

It's not necessarily thrilling or edifying to find yourself in the claustrophobic company of characters whose only occupation and preoccupation is sex and who are obviously headed for Ban End. Unless a dramatist is exceptionally skillful and sensitive, the desired effect of "There but for the grace of God, go I . . . " is likely to degenerate into "Good riddance to bad rubbish."

Oshima's film is dramatically faulty because there's never the slightest inkling of suspense about where the attraction of Sada and Kichi is leading. Even if you entered ignorant of their fates, Oshima uses such blunt foreshadowing devices and insists on such a ponderous mood that you wouldn't be in doubt for long. "Realm" never generates interest in what will happen; it's a question of when, and then how grisly.

I haven't seen Oshima's earlier movies (two of the best known, "Boy" and "Ceremony," share a bill at the Biograph today and Thursday), but Joan Mellen's recent survey of Japanese film, "The Waves at Genji's Door," indicates that they were scathing studies of Japanese family life. It's conceivable that Oshima's despair about reforming what he considered an oppressive social system may have curdled into a perverse admiration for characters who seem to defy taboos and follow their impulses to the bitter end. Anyway, it's more flattering to Oshima if one takes that view. Otherwise, it may appear that he's exposed a castration complex for all the world to see, and it's not an inspired indiscretion.