The old Indian in the movie "Little Big Man," having failed to reach the Hereafter despite inhuman patience, chanting and ceremonious hunkering, descended from his sacred hilltop to declare: "Sometimes the magic works, and sometimes it doesn't."

Jerry Rubin might have done better to wrap that little nugget between two covers, sell it as The Revolution's answer to the current male sexual dilemma and cause smiles to ripple across the land. But he hasn't. Instead, with his wife Mimi Leonard, he has written "The War Between the Sheets," which is a lot longer and does not say as much.

But then Rubin, from the time he abandoned a career as a sportswriter to become the howling yippie clown of '60s social upheaval, has leaned more toward the theatric than the useful. Even when he announced a few months back that he had taken the unlikely job of securities analyst, he explained in The New York Times why he'd done it and got himself on the "Today" show. But we remember him best for his appearance before Congress in minuteman attire, for his role in the Chicago Seven trial, and for his nonsensical ramblings that put a humorous twist on the unfunny events of the Vietnam era. We do not remember him very well as sex therapist, his latest, and perhaps most amusing, role.

The surprise is not that Rubin now proclaims himself the deliverer of American manhood from its sexual frustration with Women's Liberation. Who dared imagine where Jerry Rubin might end up when he was assuring the world that drugs, sex, burning money, rioting, cartwheels and making faces were not only acceptable but preferable to almost everything else?

The surprise is that while Rubin was extolling free sex and the overthrow of governments, he was, sexually, terribly repressed. That is precisely why he can surface now and declare: Hey, I've been there, you know? I know where you're coming from.

Allegedly, "The War Between the Sheets" is a do-it-yourself sex therapy manual for troubled males. Rubin insists it is based on his own rarefied experiences, on interviews with truck drivers, waitresses, therapists and other authorities and on the results of a questionnaire distributed to the Village Voice, Forum, Crawdaddy, Playgirl, New Sun, New Dawn, the Berkeley Barb and, presumably, anyone else who stumbled by. In other words, a decidedly random sampling. The effort originated with the Male Sexual Anxiety Research Project, designed by Rubin and Leonard to explore Rubin's cocamamie theories.

Behind his own sexual difficulties lurks Rubin's Jewish childhood, of which the reader is subjected to generous doses. Rubin's experiences with his maligned and maladjusted member -- described in rompingly painful detail -- unfold as either excruciatingly embarrassing or hilariously absurd, depending on how you look at them. Either way, they do not bear repeating.

Of course, each guru needs his own moment of revelation. Rubin's occurs with a woman he calls Rosalie, a woman who must wonder at the Wagnerian proportions she assumes in this comic epic. "Rosalie and I were unintentional victims of a place and time when the Sexual Revolution combined with the Human Potential Movement," says Rubin of those tragic events.

Over lunch at a Greenwich Village health-food restaurant, Rubin whiningly tells Rosalie: "Our relationship can never grow if you always hold out the threat of another sexual relationship."

"You never get turned on anyway," Rosalie fumes. ". . . You're impotent."

And so forth.

Not one to leave his case wanting for support, however, Rubin calls up the testimony of his questionnarie respondents. Witness this woman's intriguing encounter with the struggling male libido.

"Donna and her husband had been married for six years when in 1973, 'he asked me one night where my clitoris was. I didn't have the foggiest idea. I had yet to have an orgasm, but I thought as long as he was satisfied, it didn't matter. By the time he killed himself, I had become convinced I was a lousy sex partner.'"

Maybe she was.

Without seeming to try very hard, Rubin has managed to conceal the simple truths, tender moments, light humor and good sense that might have made his slim volume worthwhile. But, as the good chief said, sometimes the magic works, and sometimes it doesn't.