Robert Altman has easily become the center-stage star of the 1991 Sundance Film Festival, partly because his new film "Vincent & Theo" and the retrospective of his earlier work have been so well-received. But mostly because he's such an amiable, down-to-earth fellow.

There are signs that festivalgoers in Park City are a little star-starved this year, with so many cancellations by above-the-title performers who were scheduled to come but, for one reason or another, didn't show.John Sayles, whose films have been an inspiration to independent filmmakers everywhere, is certainly getting a lot of attention from the press, and Patsy Kensit, who played Mel Gibson's girlfriend in "Lethal Weapon 2" and stars in the competition film "Twenty-One," is another sought-after celebrity.

And Theresa Russell received tremendous applause when she was introduced at the Egyptian Theater Thursday night before the world premiere of her latest film, the bound-for-controversy "Whore." (The applause that followed the film was, however, much less tremendous.)

But it is Altman whose willingness to participate in various seminars and whose frankness in answering any and all questions have gained an unanticipated measure of affection from festival audiences.

After taking in Sayles' new film "City of Hope" Thursday and then subjecting himself to private interviews, Altman sat with moderator Michael Wilmington, a Los Angeles Times critic, before an audience in the festival's huge hospitality suite on the upper level of Z Place on Main Street immediately after the final screening of his "Tanner '88" series.

"Doonesbury" cartoonist Garry Trudeau, who scripted the HBO limited series and was to join him, canceled at the last minute due to illness. At one point Altman, who had been saying that Trudeau is something of a hermit when he works on his comic strip, jokingly said, "I don't know how they found out he was sick - unless his doctor called."

While intended as a forum to discuss the series, which had fictional politician Jack Tanner, played by actor Michael Murphy, running a presidential primary campaign and interacting with real-life politicians, it soon spread to broader questions about Altman's overall style in films like "M*A*S*H," "Nashville," "Three Women," etc.

Amusing and surprisingly candid, Altman may have shocked some of his audience by confessing that while he considers the little-seen HBO series to be perhaps his best work, he's not as thrilled about his most acclaimed movie, "M*A*S*H." When he spoke the title of "M*A*S*H" someone in the audience started to enthusiastically applaud, then stopped and was somewhat embarrassed as Altman finished his thought. He also said he'd like to please the critics by saying that "Quintet" is his own least favorite, "But it's not."

Other Altman comments:

- On his technique of overlapping dialogue: "There are a lot of people who don't like that - including my immediate family."

- On his discovering young, naive, non-actress Shelley Duvall in Houston, Texas, while casting "Brewster McCloud": "I didn't believe her. I thought it was an act. I was really rather rude to her."

- On working with Trudeau on "Tanner '88": "We worked very well together, but we were not a matched set - we argued a lot. I feel his stuff is a little too structured. He felt I was not structured enough."

- On the possibility of a "Tanner '92" for the next presidential primary: "I don't think anyone has the courage."

- On his personal feelings about political campaigns while making "Tanner '88": "As my knowledge of the process increased it made me a little more cynical."

After the Thursday night premiere of "Vincent & Theo," about Vincent van Gogh, Altman was onstage again with Wilmington, this time at the Egyptian Theater discussing his new film.

Altman said he didn't want to do the film at first but eventually struck a deal. "I said, `I want total artistic control, and I don't even want anyone to scowl at me.' So then I was stuck with it."

Someone asked about the scene where van Gogh cuts off part of his ear. "He didn't cut his ear off - just the lobe. We weren't trying to do a special-effects version."

In another reference to his technique of overlapping dialogue, Altman told a story about one of his first films, "Countdown," which starred a young Robert Duvall and James Caan. "Jack Warner banned me from the lot - fired me (during the film's post-production). "He said, `Fire that man - that fool has actors talking at the same time."

It was nearly midnight when the "Whore" screening was over and the discussion with Theresa Russell got under way. On the panel were the film's co-producer, Dan Ireland, and co-screenwriter, Deborah Dalton. Critic Harlan Jacobson acted as moderator.

About halfway through the 45-minute forum, which was periodically plagued with microphone and telephone foul-ups, director Ken Russell (no relation to Theresa Russell), who had canceled his personal appearance at the festival, was hooked into the conversation by phone from London, where he is working on pre-production for a new film.

It was late, the panelists and audience were obviously tired and most of the discussion was about the film's origins and the participants' feelings about the project. It wasn't until the session was nearly over that the symposium's title, "Sex in Cinema: Women - Objects or Actors," was even addressed.

While it was interesting to learn that the film sprang from a London cab driver's experiences shuttling prostitutes around the city and had originally been performed as a play - essentially a lengthy monologue - and that Theresa Russell had initially turned the part down because she was "afraid" of it, most of the audience had come expecting a rather different discussion.

Especially when, at one point, Jacobson - who appeared to be very bored with the entire event - seemed to be having a private phone conversation with Ken Russell.

Theresa Russell said early on that one reason she turned the film down was because "I seem to be getting in all these roles that have some sexual thing."

She later addressed the now-famous Meryl Streep comment that if space aliens judged our world by American movies they'd think all women are prostitutes. "I agree with . . . Meryl Streep . . . but this film is different. I don't think `Pretty Woman' showed it (prostitution) as ugly as it is - and it is ugly."

Asked about the distinctions between a movie that contains a lot of sexual material and soft-core pornography, both Russells said it has to do with erotic content. "I think it's in the eye of the beholder," Ken Russell said. "I think a lot of people will expect to see explicit sex scenes (in `Whore'), but this film does not intend to be erotic - and soft-core is. There's no eroticism, no sensuality to it.

"This film cannot be accused of being erotic soft-core pornography and `Pretty Woman' was, in a way, even though it was a `Cinderella' story."

Theresa Russell said, "The whole thing of this film is that you're a sex object in a way, but there are no erotic scenes in it. It's the most unerotic film I've seen."

Ireland said he didn't know whether the film would receive an R or NC-17 rating from the Motion Picture Association of America's ratings board but that they had no intention of cutting anything to get an R if it came to that.FILM FESTIVAL SCHEDULE

FRIDAY

Egyptian: "Straight out of Brooklyn," 10 a.m.; "Belle de Jour," 1 p.m.; "Naked Tango," 4 p.m.; "Christo in Paris," 7 p.m.; "Trust," 10 p.m.

Holiday I: "Paris Is Burning," 10 a.m.; "American Dream," 1 p.m.; "Secondary Roles," 4 p.m.; "To Sleep, So As to Dream," 7 p.m.; "The Restless Conscience," 10 p.m.

Holiday II: "The Enchantment," 10:15 a.m.; "One Cup of Coffee," 1:15 p.m.; "End of the Night," 4:15 p.m.; "All the Vermeers in New York," 7:15 p.m.; "White Lies," 10:15 p.m.

Holiday III: "Lola," 10:30 a.m.; "Absolutely Positive," 1:30 p.m.; "Privilege," 4:30 p.m.; "Slacker," 7:30 p.m.; "Stop Short," 10:30 p.m.

Prospector: "Vincent & Theo," 10 a.m.; "Whore," 1 p.m.; `Little Noises," 4 p.m.; "In the Shadow of the Stars," 7 p.m.; "After the Storm," 10 p.m.

Sundance: "84 Charlie Mopic," 4:30 p.m.; "Hangin' with the Homeboys," 7:30 p.m.

Trolley Corners: No screenings.SATURDAY

Egyptian: Documentary Grand Prize Winner, 10 a.m.; Dramatic Grand Prize Winner, 1 p.m.; "All the Vermeers in New York," 4 p.m.; "Cadence," 7 p.m.; Dramatic Audience Award Winner, 10 p.m.

Holiday I: "The New Morning of Billy the Kid," 10 a.m.; "Afternoon Breezes," 1 p.m.; Documentary Filmmakers Trophy Winner, 4 p.m.; "Bicycle Sighs," 7 p.m.; "Short Order," 10 p.m.

Holiday II: "Nashville," 10:15 a.m.; "Czech Verite," 1:15 p.m.; "Waltz in Old Havana," 4:15 p.m.; "Queen of Diamonds," 7:15 p.m.; "Zazie," 10:15 p.m.

Holiday III: "Belle de Jour," 10:30 a.m.; Documentary Cinematography Award Winner, 1:30 p.m.; Dramatic Cinematography Award Winner, 4:30 p.m.; Dramatic Filmmakers Trophy Winner, 7:30 p.m.; T.B.A., 10:30 p.m.

Prospector: "Discovery Program," 10 a.m.; "McCabe and Mrs. Miller," 1 p.m.; "Truly, Deeply, Madly," 4 p.m.; "New Jack City," 7 p.m.; "Naked Tango," 10 p.m.

Sundance: "A Matter of Life and Death," 2 p.m.; "The Enchantment," 4:30 p.m.; "Raspad," 7:30 p.m.

Trolley Corners: No screenings.