His departure ends his nearly 10 years at the helm of the glitzy magazine empire and more than 25 years at the company owned by the Newhouse family.

He will be replaced by Charles Townsend, 59, who had been the chief operating officer of the parent company, Advance Magazine Publishers Inc., as well as chief operating officer of Conde Nast.

Townsend will now be CEO of Conde Nast - publisher of Vanity Fair, Vogue and The New Yorker, among others - as well as keep his Advance duties.

Florio, who turns 55 in April, had quadruple bypass surgery in 1998 and more recently had a fainting spell while working out at his Key Largo, Fla., vacation home in early December.

He also canceled this year's "Italian Guys" Christmas luncheon, traditionally held every December, and began taking things a little more slowly at the end of 2003.

Late Friday, said Florio - whose days often started at 4:30 a.m. so he could make 5 a.m. meetings with his early-rising boss - he told Si Newhouse he no longer wanted to put in the long, hard hours.

"I need a lifestyle change," Florio said he told Newhouse.

"It wasn't something I wanted to hear," Newhouse told The Post. "We had probably the most successful year in the history of the company in ad pages and in stature."

He declined to say if it was the most profitable. "We never talk about profits," he said.

Newhouse quickly put the ball in motion, and by yesterday it was official: Florio would become vice chairman of the Advance Magazine Group.

"I go from 17 direct reports to one. I report to Si," said Florio.

Most suspected the move was tied to Florio's heart condition, but Florio insisted otherwise. He blamed his December fainting spell while exercising to dehydration.

"I'm in the best health that I've been in for years," he said.

Florio's successor, Townsend, has been quietly gaining power over the past few years.

He supervised the move to the new Conde Nast headquarters and last year oversaw a deal in which Wilmington, Del., gave the family a $1 million tax break to move a lot of its computer and back-shop operations to the city.

Townsend has also enjoyed increasing access to Newhouse over the past few years.

Florio, known to enjoy the limelight and the sway he had with Newhouse, was not always willing to share - even with a low-key executive like Townsend.

There were reports of behind-the-scenes friction. There is no serious rift between the executives, but Florio has not always been happy about the subtle shift of power.

Yesterday, Townsend insisted, "I've known Steve since 1976. There is no friction between us. We're very close friends. We spend many weekends together."

Townsend was actually brought into the company by Florio in 1994 as publisher of Glamour, and a year later was promoted to executive vice president of Conde Nast.

Earlier in his career, he had served as the president of the New York Times' women's magazines group, which at the time included McCall's, Family Circle and Child magazines. The unit was eventually sold to Gruner + Jahr USA.

Townsend started his career as an ad sales rep in Florida and worked at Hearst Magazines as a publisher and top executive before joining the Times.

He is seen as low-key and oriented toward the bottom line - a stark contrast to the blustery, swaggering Florio.