Last week Mayor Bloomberg stood with the leader of the construction unions council, Edward Malloy, to accept the endorsement of the Building and Construction Trades Council of Greater New York, a consortium of construction unions.

While the event was portrayed as handing Mr. Bloomberg the votes of 100,000 union members and the support of construction workers across the five boroughs, the victory is smaller than it might have seemed.

The question now is, where is the fight for the local unions?

Two days after the Bloomberg announcement with the Buildings Trades, the speaker of the City Council, Gifford Miller, and another Democratic mayoral candidate, Fernando Ferrer, were sitting before the endorsement committees of the painters union. The two mayoral hopefuls were talking to leaders of one of the Building Trades Council’s member unions, hoping for its endorsement as if the Trades Council’s announcement had never occurred.

“We have our own process,” the International Union of Painters and Allied Trades’ political director, Jack Kittle, told The New York Sun, saying the painters endorsement is still in play. “Mike is still in the mix, but nothing has been decided.”

Other unions are at the same stage. The Mason Tenders and the Plumbers Union, two members of the Building Trades Council are also interviewing Mr. Bloomberg’s competition and are open to wooing from the mayoral hopefuls. Some analysts said it is very possible that a roster of construction unions will weigh in on the Democratic primary, which has four people vying for the nomination, before endorsing the mayor in the general election. Mr. Bloomberg’s popularity among Building Trades unions has been greatly enhanced by his fierce advocacy for construction of the New York Sports and Convention Center – the New York Jets football stadium – which proponents have portrayed as a huge jobs generator.

In New York City, union support historically has been vital for candidates, who almost always need organizational help on the ground. The carpenters union, for example, has been seen as a must-have endorsement. The union is very active in campaigns and, because it requires members to do political work, has the ability to put thousands of members on the street.

Similarly, 1199, which represents the hospital workers; District Council 37, the largest union in the city, which represents hundreds of thousands of city workers, and 32BJ, the doormen’s local, are considered important unions to win over. The doormen are key for any candidate trying to get campaign literature into buildings.

All of those unions are still up for grabs, analysts and union leaders said, as the candidates – the mayor and Mr. Miller, of Manhattan; Mr. Ferrer, who is a former Bronx borough president; Rep. Anthony Weiner, of Queens, and the Manhattan borough president, C. Virginia Fields – make the rounds to try to win their support.

Messrs. Miller and Ferrer made a good case last Wednesday night for why they deserve the painters endorsement, Mr. Kittle said, though he declined to discuss which candidate his union is likely to back.

“We sit down the last Wednesday of every month and we’re still trying to get C. Virginia Fields to come in,” Mr. Kittle said. “I’m willing to sit down with Tom Ognibene, too,” he added, offering an invitation to the former minority leader of the City Council, who is seeking the Republican and Conservative mayoral nominations.

Mr. Bloomberg’s campaign manager, Kevin Sheekey, said this is all part of the process, and the Bloomberg campaign was well aware that the Building Trades Council endorsement was just the tip of the iceberg.

“You have to get umbrella organizations and the locals, and no one should assume that just because we got the Building Trades, that meant everyone else had signed on, too,” Mr. Sheekey said.

“That said,” he continued, “Eddie Malloy isn’t a small endorsement. He is a senior member of the labor movement in the city.”

While most candidates want unions for their organizational skills, Mr. Bloomberg’s motivation is different. He needs all the labor support he can muster before teachers, police, and firefighters make a big push against him during the fall campaign. The three municipal-labor forces have been working without contracts for years and have blamed the Bloomberg administration’s intransigence for the impasse. They are likely to be a powerful antagonist to the mayor, and he needs other unions to blunt that blow.

Similarly, the Bloomberg campaign would just as soon avoid a battle with unions over the airwaves – the latest weapon in the union arsenal. In that sense, analysts said, the role labor unions play in elections has changed. They used to be counted on for blocs of votes or for their organizational help on the ground. Increasingly, however, it is their power in the media – their ability to buy print ads or television time – that has made them a force to be reckoned with.

Consider California. Governor Arnold Schwarzenegger unexpectedly dropped his plan to overhaul public pensions last month after firefighters and police officers launched an advertising campaign against the proposal over the airwaves. Similarly, the popular Republican had to abandon his main education proposal, under which teachers would be paid according to performance rather than seniority, after teachers unions began underwriting television ads against him. Now the governor has turned his attention to teacher tenure, pressing a plan to give educators tenure after five years rather than two. The moderation in tactics was Schwarzenegger’s reaction to the unions’ clout, analysts said.

For Mr. Bloomberg, who is spending his own fortune to run for re-election, a tit-for-tat advertising battle is of less concern than the prospect of having regiments of union members on the ground for his opponent this fall. Mr. Bloomberg has the organization and volunteer network he needs on the ground, but his opponents are still trying to build that kind of grassroots machine. If Mr. Bloomberg can keep the most potent private-sector unions – the members of the Building Trades, carpenters, and doormen – in his camp, strategists said, it will make his battle that much easier come November.