The six candidates who would like to replace Mayor Bloomberg as mayor arose early Saturday morning and made their way to the New York Hilton for a candidates’ forum at the United Federation of Teachers spring conference. They all went home with a smile.

It is hard for a candidate running against the mayor to get a bad reception at this event. The mere mention of the mayor’s name was a sure trigger for a chorus of boos from the audience of more than 2,000 angry teachers.

The war between the mayor and the teachers has made the endorsement of the UFT a much sought-after commodity. Particularly in a primary, UFT mailing lists and phone banks could conceivably make a difference in the tightening race among Democrats.

Until recently, Fernando Ferrer, the former Bronx borough president, seemed to have the union nod sewn up. After all, they did endorse him in the runoff four years ago. But the declining fortunes of the Ferrer effort have put the union back in play, and the UFT could either endorse, or perhaps not endorse, a candidate in the primary.

Among the Democrats, the biggest applause was for Rep. Anthony Weiner, who has been scoring points in these live forums across the city. Mr. Weiner frequently pointed out that his mother was a teacher and he got a particularly strong response when he vowed to “respect the due process rights” of students suspended for misbehavior, but not nearly as much as protecting the “rights of the other 34 students” in the classroom, whose educations were being disrupted by unruly classmates.

A close second was Council Speaker Gifford Miller, whose proposal to cap class size at 17 was music to the ears of the assembled membership. Bringing up the rear were Mr. Ferrer and C. Virginia Fields, the borough president of Manhattan. Surprisingly, Mr. Ferrer is still pushing his proposal for a stock transfer tax, an idea almost universally derided as unworkable.

Right now, the smart money would be on the union’s waiting to see who wins the Democratic primary. No one is discussing what could be the most effective way for the UFT to get at Mr. Bloomberg – an effort to lift one of the cash-starved GOP candidacies, presumably Thomas Ognibene, a former Council member.

The UFT phone bank could be a huge advantage in a Republican primary where a swing of a small number of voters could be decisive. A loss of the Republican line for Mr. Bloomberg would be a crippling blow. At the very least, a serious race in the Republican primary forces Mr. Bloomberg to cover his right flank in September, perhaps providing red meat to the Democrats who seek to exploit the downside of his Republican Party affiliation in November.

Mr. Ognibene, whose wife and mother were both teachers, was well received by the teachers on Saturday. Despite his credentials as a very much right-of-center Republican, his bearing and style seem to resonate with audiences that should be antagonistic. Mr. Ognibene cited his own experience on the board of a private school, noting that he raised the salaries of his teachers by 22%. This got the attention of the audience.

But when Mr. Ognibene noted that disruptive students in his school are expelled, implying that this might be a strategy for the public schools (to which his former pupils were presumably exiled), the assembled teachers were shaking their heads. They were wondering where children expelled from public schools would go.

The other Republican in the race, investment banker Steve Shaw, was cordially received but produced audible groans when he suggested the end of all rent regulations.

None of the mayoral candidates stayed for the lunch, which began with a call to arms by the union president, Randi Weingarten. A number of elected officials, including Comptroller William Thompson, Public Advocate Betsy Gotbaum, Rep. Charles Rangel, and Rep. Major Owens were on hand to hear Ms. Weingarten denounce Mr. Bloomberg and Joel Klein, the schools chancellor, in the strongest possible terms. Neither the mayor nor the chancellor attended this year’s function. The most senior Department of Education official present was Deputy Chancellor Carmen Farina, who, I am sure much to her relief, was not introduced. In an otherwise uncompromising attack, Ms. Weingarten left the door ever so slightly ajar for a possible contract settlement. “It is not too late for us to work together to fix what is broken and to expand what works,” she said. “Instead of regretting the past, we can build the future.”

After the main course came the highlight of the program, the presentation of the union’s John Dewey Award to education historian Diane Ravitch. This is no small honor, as the list of former recipients includes Eleanor Roosevelt, Herbert H. Lehman, Thurgood Marshall, Martin Luther King Jr., Henry M. Jackson, Hubert H. Humphrey, Daniel Patrick Moynihan, Jacob K. Javits, and President Clinton. A minute cadre of union dissidents had complained of Ms. Ravitch’s selection, characterizing her as a “right-winger,” presumably for her service in the administration of the first President Bush and her support of traditional pedagogy.

In accepting the award, Ms. Ravitch did not disappoint anyone in this anti-Bloomberg crowd, which rewarded her with a standing ovation. If anything, her criticism of the mayor’s stewardship of the city’s school system was even harsher than Ms. Weingarten’s.

Ms. Ravitch spoke of the history of the teachers union movement in New York, noting that the most frequently criticized protection of teachers’ rights, tenure, was a 19th-century invention that long predated the establishment of even the earliest teachers’ union. In criticizing the Tweed regime, and the poor relations that have developed between the administration and the teachers, Ms. Ravitch concluded, “The lesson of history is as clear today as it was in 1916: Teachers need their union. And so, I might add, does the public.”