Mayor Bloomberg’s deputy mayor of operations, Marc Shaw, has resigned and accepted a top job at the Extell Development Company, a Manhattan based real estate giant that entered a rival bid to Bruce Ratner’s plan to develop downtown Brooklyn.

Mr. Shaw, who has 25 years of government experience and is considered by some to be a financial guru, is the fourth key member of Mr. Bloomberg’s team to leave City Hall for a more lucrative paycheck in the private sector since Mr. Bloomberg’s re-election.

Although his resignation has been expected for a more than two months, it is added to the revolving door of seemingly amicable departures that has also included the mayor’s chief of staff, Peter Madonia, his communications director, Bill Cunningham, and another deputy mayor, Ester Fuchs.

“It’s a natural transition,” Mr. Shaw, 51, told The New York Sun yesterday during a telephone interview. “I decided to do this some time ago and I was waiting until after the election to serve out the first term. It’s the normal reasons of kids growing up, going to college.”

Mr. Shaw has three sons; his oldest is a junior at the Massachusetts Institute of Technology, where tuition, board, and dining cost $41,800 a year, according to the school Web site.

Mr. Shaw, who was earning $213,391 as first deputy mayor, will undoubtedly get a significant salary boost at Extell, which is one of the largest development companies in a city where the hottest industry is development. He would not disclose his new salary, joking that after 25 years in government, “It’s no longer public.”

Mr. Cunningham is now in a senior position at Dan Klores Communications, a powerhouse public relations firm; Mr. Madonia is the new chief operating officer at the Rockefeller Foundation, which has a $3 billion endowment, and Ms. Fuchs returned to the faculty position she left at Columbia University when she joined the Bloomberg administration.

The mayor has replaced most of his departing advisers with members of his inner circle who have been with him since before he ran for office. Two of his top aides, Kevin Sheekey and Edward Skyler, were recently named deputy mayors, and Patricia Harris, who is said to be the mayor’s closest professional confidante, was promoted to Mr. Shaw’s “first deputy” position.

Mr. Shaw – who served as executive director of the Metropolitan Transportation Authority and as Mayor Giuliani’s director of management and budget – and the others who have departed are credited with helping the first-term novice politician get a handle on the city’s $50 billion budget and web of agencies.

“For the last four years, New Yorkers have reaped the dedication and talent of Marc Shaw,” Mr. Bloomberg said yesterday in a statement. “As first deputy mayor, Marc was a shrewd and steady hand that helped guide New York through its worst fiscal crisis in a generation.”

The mayor also said many of his administration’s successes, including winning control of the city’s school system, bear Mr. Shaw’s fingerprints.

A professor of public affairs at Baruch College, David Birdsell, said it was a logical time for senior members of the administration to leave and that second-term departures are common in all administrations.

He also said the staff members now exiting are at their “best marketability” and have “more leverage in terms of where they want to go.” Mr. Shaw said the mayor had put together a “great team,” but that he now has four years of experience under his belt. Extell has worked on dozens of high-profile projects throughout the city and put in a failed bid to rival Mr. Ratner’s Atlantic Yards proposal in Brooklyn.

Mr. Shaw said yesterday that he had not yet talked to the mayor about staying on as one of his appointees on the Lower Manhattan Development Corporation.