The four Democratic mayoral contenders are scheduled to meet tonight in the first official debate of the primary season.

Mayor Bloomberg, a Republican, will be nowhere near Jazz at Lincoln Center, the debate venue, and told reporters yesterday he wouldn’t be blocking time out in his evening to view the exchanges among the Democrats who are vying for his job. He also said he wouldn’t record the debate to watch later. The debate, from 7 to 8:30, is being shown on NY1. The Democrats face off again Sunday, live on CBS-TV at 11 a.m., though that debate is not sanctioned by the city’s Campaign Finance Board. The next city-approved debate is September 7.

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The Conservative Party’s mayoral candidate, Thomas Ognibene, will attempt today to convince a federal judge that he should be allowed to run as a Republican, too.

Mr. Ognibene is suing in federal court at Brooklyn to force a GOP primary September 13, the candidate said yesterday. Mr. Ognibene, a lawyer, said his case would rely on proving that the state’s ballot-access laws violate the First and Fourteenth Amendment rights of the city’s Republicans.

Mr. Ognibene collected 8,100 signatures on petitions asking that he be placed on the Republican primary ballot, but the Board of Elections, acting on a challenge from the Bloomberg campaign, determined that only 5,700 were legitimate. Mr. Ognibene needed at least 7,500 valid signatures. He argues that in a city with relatively few enrolled Republicans, it is nearly impossible for “non-wealthy-incumbent” Republicans to run for citywide office. The lead plaintiff in his suit, Mr. Ognibene said, will be Eric Ulrich, an Ozone Park, Queens, resident who carried petitions for Mr. Ognibene and is himself a candidate for state Republican committee from the 23rd Assembly district.

As Mr. Ognibene prepared yesterday for his federal case, a judge of state Supreme Court at Manhattan, Jacqueline Silbermann, dismissed the Bloomberg campaign’s lawsuit challenging the validity of Mr. Ognibene’s ballot-access petitions. Parties to the case said yesterday that Justice Silbermann had determined that the Board of Elections ruling made it unnecessary to hear the case in court.

Ms. Silbermann also ruled yesterday against the former Independence Party official challenging Mr. Bloomberg’s signatures to appear on that party’s ballot line, Michael Zumbluskas. The judge cited Mr. Zumbluskas’s failure to inform Mr. Bloomberg of his challenges to his petitions by certified mail.

Mr. Zumbluskas said yesterday that he plans to appeal.

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Mayor Bloomberg won the coveted endorsement of the city’s largest municipal union, District Council 37, but one of his opponents snagged the backing of the union’s retirees yesterday.

During a news conference yesterday, officials of the 50,000-member Retirees Association of DC 37 announced that it would back the speaker of the City Council, Gifford Miller, in his bid for mayor.

The DC 37 endorsement was a huge coup for the mayor, as the union represents roughly 121,000 non-uniformed city workers, and its backing signaled to other labor leaders that it was okay to endorse a Republican. But the retirees, who are off the city payroll and already receiving pensions, did not heed the signal.

“Gifford Miller is the candidate to lead our city into the future,” the president of the association, Stuart Leibowitz, said in a statement.

A spokeswoman for DC 37, the umbrella union for 56 smaller unions, said the retirees were “autonomous from us.”