By Sheldon Kirshner

At a Passover seder 21 years ago in Manhattan, Ira Wohl sat next to his mentally disabled cousin, Philly Wohl, whom he liked but had never really taken notice of.

That night, Philly, normally sociable, was in a particularly garrulous mood, and his ebullience grated on his aunt's nerves.

"Shut up, already," she said, unmindful of Philly's sensitivities.

The incident unsettled Ira, a filmmaker who started his career as an editing-room assistant to Orson Welles.

"It struck me that Philly was a real person, and it made me wonder what would happen to him when his parents were gone," explained Wohl, now a psychotherapist practicing in Los Angeles.

As he thought about Philly's future, Ira Wohl decided that a movie about his quest for greater independence would be appealing to a mass audience. Hurriedly gathering together a crew to shoot the first scene, at Philly's doctor's office, Wohl embarked on a project which would culminate in Best Boy, his award-winning documentary.

Four years in the making, the heartfelt Best Boy won the 1980 Oscar for best feature documentary and captured first prize at festivals in Toronto, Miami, Houston, Chicago, New York and San Francisco. Best Boy, too, played theatrically and on television all over the world, including Israel.

After Best Boy, Wohl produced and directed a variety of TV shows, notably a series for teenagers on the Nickelodeon network. Last year, after a family visit to New York, Wohl began to think in terms of doing a sequel to Best Boy.

"I hadn't seen Philly in a while, and I was struck by how much his life had changed since Best Boy. He was a different person, much more self-confident. It made me want me to know more."

And besides, he added, "people were still asking me about Philly, wondering whether he was alive."

Soon enough, Wohl was back documenting Philly, now 70, in Best Man: 'Best Boy' and All of Us Twenty Years Later, which premiered at the recent Toronto International Film Festival.

Funded by American, British and French TV networks, the 90-minute film charts Philly's progress in a group home, following the death of his parents, and documents his affecting relationship with his sister Frances, his surrogate mother. Best Man, which Wohl calls a film about "the value of family," climaxes with a ceremony in which Philly is bar mitzvahed in a Manhattan Conservative synagogue.

Touchingly, Wohl describes it as "a bar mitzvah for a son I never had."

Philly, he disclosed, delighted in making Best Boy and Best Man, which is currently being screened across America. "It was never a problem getting him to cooperate," said Wohl. "He loved me and the crew to be around him. And he trusted the idea."

Wohl did not let him down. Philly liked Best Boy, if only because he associates it with a sense of camaraderie and the good food at the wrap party.

Philly has yet to see Best Man. But Wohl is confident he won't be disappointed. "I think he'll enjoy it. It was a good experience for him."

Considered by psychiatrists to be "very slow but normal," Philly has a "happy and full life," in Wohl's estimation. "He can live in the group home for as long as he lives. His life is set."

Philly's IQ is in the 30-to-40 range. "But his IQ doesn't tell you about his personality," adds Wohl. "He's a very highly socialized person."

Philly, as well, is quite aware of his Jewishness, though Wohl does not know how he filters it through his consciousness. "On an emotional level, he understands the concept of the bar mitzvah, maybe more than we all do."

Although he left the film business several years ago, after concluding he would be happier in psychotherapy, his first love, Wohl had not entirely jettisoned it. Two years ago, he combined both professions by making a documentary about psychological diagnosis. And now he is planning two new documentaries, the first about heroin and the second about the last Orthodox Jewish community in Mississippi.