Tina Brown, the celebrity editor who transformed the New Yorker from a fading cultural institution to a fiercely topical, sometimes glitzy magazine that continued to hemorrhage money, stunned her staff yesterday by announcing her resignation.

Brown will become chairman and part owner of a new multimedia company, in partnership with Miramax Films, that will launch a monthly magazine and produce movies, television programs and books.

S.I. Newhouse, whose media holdings include the New Yorker, offered Brown millions of dollars to sign a five-year contract, but after staring at it, she told her staff, "I couldn't stand the thought of getting married for five more years."

Brown's confidants say she has been frustrated by plans to merge the New Yorker's operations into Conde Nast, the Newhouse magazine empire, and by the company's refusal to let her launch other media ventures. She has also been deeply affected by the death of her mother, who urged her to get more fun out of life, just days ago.

"It was so difficult to make the decision because of my great passion for the New Yorker," Brown, 44, said in an interview. She said her friend Harvey Weinstein, co-chairman of Miramax, "was offering something the New Yorker couldn't offer me: equity, a partnership, the ability to create a new media company."

Conceding that the New Yorker had become less of a challenge, she said: "I was having a lot of doubts about it, and agonizing over it, and wanted to do it and then felt I shouldn't. That psychological moment is when Harvey moved in."

In a larger sense, the British-born Brown, who made her name editing Vanity Fair before joining the New Yorker in 1992, has been a master practitioner of "buzz," the magical chatter that renders a publication must reading. This is the woman who once put a naked and very pregnant Demi Moore on Vanity Fair's cover. But the buzz on Brown has grown rather negative of late, particularly as her magazine lost a reported $60 million in the last four years.

"Even a brilliant person has only so many ways to do a weekly," said Kurt Andersen, a New Yorker writer. "The second 300 issues are probably going to be less original and surprising and interesting to the world and yourself than the first 300."

"She gets a lot of criticism for being obsessed with buzz, but buzz is what brings you to the magazine," said Michael Kinsley, editor of Slate. "She saved that magazine, editorially. It's the hottest magazine being published."

There was no immediate morning line on a successor, since Brown didn't give Newhouse her decision until 9 a.m. yesterday. Those being touted include Graydon Carter, Vanity Fair's editor; Kinsley, a former editor of the New Republic and Harper's; Andersen, a former editor of New York magazine; and David Remnick, a Pulitzer Prize-winning New Yorker writer.

Brown, who says she had several other offers, is the second member of her family to leave Newhouse's privately held corporation. Her husband, Harold Evans, resigned last year as president of Random House under less than happy circumstances.

The new Miramax venture, whose market appeal remains to be seen, is the logical extension of Hollywood's constant scouring of books and magazines for movie ideas. Bidding wars frequently break out over the rights to hot new books even before they go to press, and magazine pieces are commonly mined for script ideas.

Once a scrappy independent studio, Miramax was bought five years ago by Disney and now churns out more films than most of its rivals, including such hit movies as "Good Will Hunting" and "The English Patient." Weinstein noted that "Saturday Night Fever" and "Urban Cowboy" began as magazine pieces.

Calling the venture "incredibly exciting," he said: "We can find a way to create a one-hour television special around a brilliant nonfiction piece, or it could become the basis of . . . movies. It's all about content."

Weinstein said he had gotten Disney's approval to create a magazine two years ago. He said the magazine "is going to be much smaller on a financial level than everyone thinks."

Engaging in a bit of advance buzz, Brown said her new monthly would be "a sizzling, 21st-century magazine" that would be "sophisticated" and "upscale." She will be joined as president of the new media firm by Ronald Galotti, who was her publisher at Vanity Fair and now is publisher of Vogue, another Conde Nast publication.

As recently as a week ago, Brown was telling friends she would sign another New Yorker contract, but she cut the Miramax deal at 5 p.m. Tuesday. There was some talk yesterday that Newhouse precipitated her exit by insisting on a long-term deal and perhaps other concessions.

Brown gave her senior editors the news in a sad voice at a planning meeting for an October issue on the future, which was to be accompanied by a Las Vegas conference. Several women editors cried, and Brown hugged each of her colleagues.

"It's sometimes grueling to work with her, but also exhilarating," said Jane Mayer, a Washington-based staff writer. "She's very exacting. She doesn't have a boring bone in her body."

While Brown's friends are "thrilled" for her, said Ken Auletta, the magazine's media writer, "the flip side is a concern for what happens next at the New Yorker. What happens to the people on staff?" One reporter said Brown's departure "makes the whole place feel like stale goods."

"We don't have that many cultural institutions around that we can allow this one to die off or become jellied in aspic," Remnick said. "There's no point in a New Yorker that's just okay or trades on its own past."

Brown's future became the subject of considerable speculation in late May when Steven Florio, Conde Nast's chief executive, removed the New Yorker's publisher -- who happens to be his younger brother, Thomas Florio -- without consulting her. Brown was said to be clashing with the senior Florio over such decisions as the one to bring the magazine into the corporate fold and move the New Yorker from its West 43rd Street offices to a new Conde Nast building in Times Square.

And there were media reports that seemed to blame Brown's free-spending ways -- she has been known to pay as much as $25,000 for an article -- for the magazine's financial distress. Perhaps the most bruising was in Fortune, which called the New Yorker "one of the greatest money pits in American magazine history" and savaged Steve Florio for exaggerating parts of his background, including claims that he had once played minor league baseball and served in the military.

Asked if she shared responsibility for the New Yorker's sea of red ink, Brown said: "It depends on what you define as the editor's job. I personally think the editor's job is to create a brilliant magazine. It's the publisher's job to sell advertising, not my job. My job is to bring in content, to bring in talent."

And she recruited plenty of high-priced talent while dumping some of the old guard, many of them established authors. Backed by an expensive promotional campaign, Brown boosted circulation from 628,000 to 809,000 and won 10 National Magazine Awards for such pieces as Connie Bruck on Newt Gingrich, Adam Gopnik on Pablo Picasso, plus short fiction by the likes of John Updike, Alice Munro and Cynthia Ozick.

From the day she took the job, the onetime editor of London's Tatler was assailed by some for trampling on the hallowed traditions of legendary New Yorker editor William Shawn.

"The magazine had become old and in some ways ossified," Auletta said. "The regime before Tina basically acted like a museum curator. She was determined to make it more relevant. She made some mistakes, published some pictures that some of us were not that thrilled with. But she did a brilliant job."

Brown's tenure did not produce much journalism with the long-term cultural impact of the most memorable New Yorker stories -- Rachel Carson's "Silent Spring," John Hersey's "Hiroshima" or Truman Capote's "In Cold Blood." However, she published plenty of provocative pieces on foreign affairs (Richard Holbrooke on Bosnia, Remnick on Bibi Netanyahu), law (Jeffrey Toobin on sexual harassment statutes), politics (Joe Klein on Al Gore), media (Auletta on Don Imus), culture (Jorge Luis Borges on Shakespeare) and investigative reporting (Mayer on Linda Tripp's 1969 arrest, which sparked a Pentagon probe of how she got the information).

There were low moments as well, from the women's issue guest-edited by Roseanne to the piece about the trial of former East German leader Erich Honecker written by the wife of Honecker's lawyer. There were the photos of Kato Kaelin during the O.J. Simpson case and the graphic article on the life of a dominatrix. Brown herself contributed a gushy piece about President Clinton after a state dinner ("his height, his sleekness, his newly cropped, iron-filing hair, and the intensity of his blue eyes") and one on her friendship with Princess Diana after Di's death.

The result was a tough sell to advertisers, and as the New Yorker grew noticeably smaller, there was grumbling that Brown had made it more like every other trendy magazine. Brown dismissed the carping, citing advice from the late New Yorker writer Harold Brodkey on her first day. "Beware of New Yorker fakery," she recalled him saying. "All these people will say to you, it's not what it was, it's become too this, too that. They've been saying that for 50 years."

But perhaps Brown was simply restless, as reflected by her parting comment: "When something's perfect, it always seems like a good time to leave." Staff writer Sharon Waxman in Los Angeles contributed to this report. CAPTION: Tina Brown says Miramax "was offering something the New Yorker couldn't . . . equity, a partnership."