Mayoral contenders will learn Wednesday who among them has earned the coveted United Federation of Teachers endorsement, with the decision coming a day after Bill Thompson secured the nod from the allied principals' union.

Thompson, a former city comptroller and board of education president, Tuesday declined to speculate about whether he will be the UFT's pick during a conference call about his Council of School Supervisors & Administrators endorsement.

"This endorsement is about CSA . . . and how proud I am to have their help and their support in the campaign," Thompson said. "It isn't about Mike Bloomberg's comments or speculation about anything else."

Bloomberg on Monday equated the UFT's endorsement with a "kiss of death," noting the union's last winning mayoral pick was Democrat David Dinkins in 1989. Bloomberg has long butted heads with the union, which has 200,000 members.

Bloomberg and the union failed in January to reach a deal on a teacher evaluation system, costing the city $250 million in state and federal funds. The mayor also has ruled out retroactive raises, angering UFT members who have been working since 2009 without a contract.

Still, UFT support could be critical for Democrats seeking a boost in this year's crowded primary.

The UFT will announce its endorsement at 5:45 p.m. at its Financial District headquarters, after the union's administrative committee, executive board and 3,400-member delegate assembly cast ballots.

UFT president Michael Mulgrew declined to comment Tuesday, but he has told Newsday he believes the UFT's pick will be the election's winner.

advertisement | advertise on newsday

Besides the CSA nod, Thompson is backed by American Federation of Teachers president Randi Weingarten, formerly a UFT president, and state Regents Chancellor Merryl Tisch.

Ernest Logan, president of the 16,000-member CSA, said his group chose Thompson for his plans to bolster housing and jobs along with education.

Public Advocate Bill de Blasio, Comptroller John Liu and City Council Speaker Christine Quinn -- who have split other labor support -- have like Thompson been courting the UFT.

David Birdsell, dean of Baruch College's School of Public Affairs, said there's no clear choice for the UFT. It could gravitate toward Liu and de Blasio for their emphasis on traditional public schools, but could choose Thompson, Quinn or former Rep. Anthony Weiner as candidates who are more likely to make a Democratic runoff in September.

"The UFT might wind up exactly on the other side of the equation," he said. "But the point of pain for them is going to be the political viability of a Liu or de Blasio candidacy."

With Matthew Chayes