"Fahrenheit 9/11," director Michael Moore's scathing attack on President Bush and the administration's response to the terrorist attacks of Sept. 11, 2001, was the hottest film in America over the weekend. If early estimates are correct, the movie instantly became the top-grossing documentary in the nation's history.

The film is believed to have earned $21.8 million on its opening weekend, a record for a documentary. Even more significantly, it managed to become the nation's No. 1 movie attraction, despite playing on only 868 screens, about a third what a big blockbuster would have.

"It became part of the national conversation this weekend," Moore said during a morning conference call yesterday.

"This is one of the events of the summer," said Paul Dergarabedian, president of Exhibitor Relations, an independent company that tracks box office returns. He said he was particularly impressed with the per-theater average of $25,115: "I'm amazed at those numbers. That type of per-theater average is usually reserved for a blockbuster."

It was actually a tad lower than the $26,144 per screen for Moore's previous documentary, "Bowling for Columbine," but that film opened at just eight sites in October 2002, and eventually reached only 248 locations, despite winning an Oscar. The anti-gun movie has grossed $21.5 million -- a record for a documentary but less than the haul for "Fahrenheit 9/11" from Friday through yesterday.

"Fahrenheit's" opening was the highest ever for a movie under 1,000 screens, and the third-highest screen average of the year, behind only Mel Gibson's "The Passion of the Christ" and the animated family film "Shrek 2." In second place this past weekend was the comedy "White Chicks," starring the Wayans brothers, popular with urban audiences. The PG-13 Sony film played at 2,726 theaters over the weekend, averaging $7,190 per screen for a $19.6 million gross.

Initially, Hollywood analysts predicted only a modest $10 million opening for the Moore film. The documentary was dumped by Disney, its distributor, despite winning the top award at the prestigious Cannes Film Festival. But as the pro and con buzz built, $15 million was the sum bandied about. After the movie had sold-out premieres at two theaters in Manhattan on Wednesday, upward of $20 million was considered likely.

By Friday morning, many evening showings around the country were already sold out. Checking his computer that morning, Jeff Kaufman, vice president of Memphis-based Malco Theatres, reported sellouts for both early evening shows at the one of his local theaters, which generally plays high-end commercial and art films, but had sold only five advance tickets at a multiplex in suburban Memphis. However, he said, "I don't think this movie is going to play like a documentary. I think it's going to play a little bit more broad-based. I think the film has a tremendous amount of want-to-see. . . . It's getting probably more publicity than any other documentary in history, both paid and media."

By Friday evening, officials at Lions Gate Films Releasing and IFC Entertainment -- which had collaborated with producers Harvey and Bob Weinstein's newly created Fellowship Adventure Group to get the film distributed following Disney's bow-out -- knew the record book was being rewritten.

By yesterday morning they were ecstatic.

Tom Ortenberg, president of Lions Gate, joined Moore on the conference call. "The film played brilliantly this weekend in the 'red states' and the 'blue states,' and the big towns and the small towns," he said. "We played in Peoria. We literally sold out Peoria, Illinois."

Surveys showed the audience was split evenly between male and female, and was predominantly over 25. The biggest demographic consisted of moviegoers aged 25 to 34. In exit polls conducted in about 15 cites, 91 percent of the audience rated the film "excellent," and 93 percent would "definitely recommend" it.

"It's mind-blowing how well this film has been received," said Jonathan Sehring, president of IFC, noting that exit polling for "Fahrenheit" was even better than for the 2002 surprise hit "My Big Fat Greek Wedding."

The exit polls did not survey political affiliation, but Sehring said he knew of sellouts in Long Island's Nassau County, "long considered a Republican stronghold." He also reported that his 17-year-old son (old enough to get in, given the R rating) witnessed a standing ovation from the audience at a mall theater.

The film packed theaters in Washington, where most evening shows were sold out. Bob Zich of the Avalon Theatre said he wasn't sure of the politics of the moviegoers but guessed that "most of them probably knew about the notoriety of the film" and that they were "probably mostly Democratic partisans."

Matt Cowal, marketing manager for Landmark Theatres in Washington, said the movie is doing "phenomenally well" at his chain's downtown and Bethesda complexes. Most evening shows have been sold out and some audiences have been cheering during the movie, he said.

The screenings yesterday afternoon at the Loews Georgetown were sold out. Dozens of people milled about on the front steps, waiting an hour or more for the next available showing.

Jim Lenihan, 23, a recent Georgetown University graduate, had switched to an evening screening because the afternoon show he planned to see had sold out before all his friends had bought tickets. "I think he [Michael Moore] is very good at expressing his opinion through facts," said the Detroit native, who said he has seen every Moore movie since 1989's "Roger & Me." "But sometimes he slants his information and he misleads, which is the same accusation he makes against Bush."

Anthony Branch, 29, a bartender, said the movie helped him better understand "what's really going on. . . . I feel he [Bush] just lied about everything."

Jim Welsh, 65, drove more than 120 miles from his home in Salisbury, Md., to see the movie. The editor of a film and literature magazine, Welsh said, "I'd like to see for myself Mr. Moore's methods and message, unlike those right-wing people who will trash it without having a clue what it involves."

Kitty Dana, 48, said she cried through two-thirds of it. "It was incredibly moving, not just satirical," said Dana, who works for the American Friends Service Committee, an antiwar group.

"It says a little about American arrogance and power," said Chandra Pant, 51, of Delhi, India, who was visiting the Danas.

Bush-Cheney campaign spokesman Scott Stanzel had no comment on the box office numbers, but suggested that those wanting another view visit www.GeorgeWBush.com and see a compilation of clips titled "Kerry Coalition of the Wild-Eyed." In general, the campaign has said it did not want to take on Moore because it would lend him credibility.

Moore made no apologies for his partisanship. "Documentaries by their very nature are supposed to have a point of view," he said during the conference call. He calls his documentary "an op-ed piece -- it presents my opinion based on fact." He said he believes the movie is playing strongly in Middle America, and that it has confounded theories that "it would only speak to the choir."

"The documentary filmgoing audience is not that large. . . . I would imagine tens of thousands of people came this weekend who had never been to a documentary in a movie theater in their lives," says Moore.

The distributors say they plan to add a couple of hundred theaters this coming weekend, and additional theaters the following weekend. By then the competition will include one of the summer's anticipated blockbusters, "Spider-Man 2."

"We look forward to joining with 'Spider-Man' to bringing truth and justice all across America," Moore said.

Staff writers Lila Arzua and Bob Thompson contributed to this report.

"Fahrenheit 9/11," which earned an estimated $21.8 million during its first three days, "became part of the national conversation," says Michael Moore.Director Moore autographs a moviegoer's ticket stub yesterday in New York.