Mayor Bloomberg, enjoying the advantages of incumbency, does not plan to start looking for office space or to hire staff for his 2005 re-election campaign until next year, aides said.

“There won’t be a campaign that anyone will recognize as a campaign until January or March,” Mr. Bloomberg’s communications director, William Cunningham, told The New York Sun. “He doesn’t need to raise money, and that’s why most campaigns start so early, so instead he can just concentrate on his job.”

Incumbents generally have the luxury of declaring their candidacies late in the game because they are a known quantity. Mr. Bloomberg seems to favor late announcements in any case: During his first run for office, in 2001, he didn’t formally declare until June 5, just five months before the election.

“Presidents have a Rose Garden strategy. Bloomberg is using a Blue Room strategy,” said an adviser to City Council Speaker Gifford Miller, referring to the room in City Hall where the mayor makes his big announcements. “It is what incumbents do.” Mr. Miller, is likely to seek the Democratic nomination to oppose Mr. Bloomberg.

Mr. Miller, for his part, began ramping up his campaign over the summer. He is leasing campaign office space on Nassau Street, has set up a Web site for contributions, and has hired several fund-raisers, advisers said. He is not expected to announce his candidacy formally until the beginning of next year at the earliest, an aide told the Sun.

In general, candidates are motivated to declare their intentions to run for office for a very basic reason: fund-raising. When they formally announce, it makes it easier to solicit and receive contributions. The field mulling whether to challenge Mr. Bloomberg has to factor in the prospect of facing an incumbent with bottomless pockets. The mayor, whose personal wealth is estimated as $5 billion, spent $75 million of his own money in the last election and did not solicit contributions. He has already said he intends to spend his own money to finance his 2005 race.

Financial considerations aside, Mr. Bloomberg comes to next year’s race with a roster of advantages. He won’t have to introduce himself to the electorate, because by Election Day they will have watched him day in and day out for nearly four years. He will not need to draw up position papers, because the job he has done speaks for itself. He may not have a challenger for renomination, because primaries are much rarer in the Republican Party than in the Democratic Party in New York.

That means, theoretically, Mr. Bloomberg could safely put off formally announcing his candidacy until well into the new year, analysts said.

“Bloomberg can put an operation together pretty quickly,” a Democratic political consultant, Hank Sheinkopf, said. “It is smart politically for him to just wait. He gets free press every day, because he is the mayor and whatever he does is news. There’s no need to start a formal campaign because it will just lead everyone to look at what he does through a purely political lens.”

The Marist Poll recently put Mr. Bloomberg’s approval rating at about 42% – six percentage points below where Mayor Giuliani was at this point in his first term. Still, the numbers are far more encouraging for Mr. Bloomberg than the 32% approval ratings that Marist recorded earlier this year. Generally, if there isn’t a hue and cry among voters to throw a mayor out of office, he is likely to win another term, analysts said.

While voters don’t particularly like Mr. Bloomberg, they typically will concede that he has managed the city well. That is why the mayor is going to great pains to focus on his record and has publicized his own report card of campaign promises kept.

It is unclear who will challenge Mr. Bloomberg in November. The Democratic field could end up with as many as three candidates in addition to Mr. Miller in the primary.

The former Bronx borough president, Fernando Ferrer, has made clear he intends to run. He has not yet set up a campaign office, but he is raising money and, in hopes of tapping into younger voters and stirring up a regional grass-roots campaign, has hired Web site gurus who worked for presidential hopeful Howard Dean. Mr. Ferrer has said he will make a formal announcement shortly after the presidential election.

In an interview with the Sun last month, the city comptroller, William Thompson Jr., said he still hadn’t decided whether he would throw his hat into the ring. He has said he will make a decision by the end of the year. Mr. Thompson has a fund-raising operation, through consultants to the campaign, but there is no formal staff or office. He may decide to defer a mayoral run and seek all-but-certain re-election.

Two other possible candidates are a Brooklyn congressman, Anthony Weiner, and the Manhattan borough president, C. Virginia Fields.

Mr. Weiner has made no secret of his intention to run. He has been raising money and has carefully sent back contributions that were earmarked for a congressional campaign, asking donors to send him the money so it would be eligible for a city campaign. Aides did not return repeated phone calls to discuss the state of campaign planning and his timetable for a formal announcement. He is the one candidate who could retain his current office if he lost a mayoral campaign. In response to an inquiry from the Sun, a Weiner aide, Kaye Anson, said yesterday: “The congressman has opened an exploratory committee for citywide office. He’s doing all of the things necessary to prepare should he decide to run.”

Ms. Fields, for her part, has quietly hired a campaign manager and is looking to increase her citywide profile. She has hired a fund-raiser and has been meeting with people to begin drawing up position papers. She has said she will make a decision before the end of the year. Aides, who declined to be identified further, said they expect she will announce her intention to run shortly after next month’s presidential election. Ms. Fields has already raised about $1 million.

With such a crowded Democratic field, analysts said Mr. Bloomberg could afford to stay on the sidelines for now.

“The mayor could wait until next September to establish a campaign office and he’d still not be too late,” the head of urban research at CUNY, John Mollenkopf, said. “He is in the public eye all the time, and his top strategists are on the public payroll and they sit right next to him.”