Randi Weingarten, the president of the New York City teachers' union, announced yesterday the start of an expansive campaign to build public support for smaller class sizes that will include advertising on television and the Internet, picketing outside schools and the celebrity endorsement of Frank McCourt, the Pulitzer Prize-winning author and former teacher.

During a speech at the union's annual spring conference, Ms. Weingarten told about 2,700 teachers at the Hilton hotel in Midtown that the moment was right for a formal push on the matter of class size in public schools. She said the union, the United Federation of Teachers, would commit $1 million to the campaign, which is backed by a wide coalition of parents and civic groups known as New Yorkers for Smaller Classes.

"The city's largest school construction program has just been funded," Ms. Weingarten said yesterday during her speech. "A gubernatorial election is coming up. And there is only one court battle left in the Campaign for Fiscal Equity lawsuit, the 13-year-old case that charges that our school kids are being shortchanged.

"It's up to us to convince the powers that be not to squander this opportunity on short-term quick fixes," she added. "Reducing class sizes is a long-term investment that must start now."

Schools Chancellor Joel I. Klein sat near Ms. Weingarten on the dais and exchanged remarks with her, but did not formally address the union.

After Ms. Weingarten's speech, the Department of Education issued a statement. "There was a lot in Randi's remarks to agree with," it said. "We have different approaches for resolving the city's class-size problem, but were gratified that she linked class size with the need for a quality teacher in every classroom."

One goal of the movement is to get a class-size referendum on a ballot so voters can decide whether a portion of the expected money from the Campaign for Fiscal Equity suit should be set aside to lower class sizes. ( Last month, education advocates appealed to the state's highest court, the Court of Appeals, asking it to force lawmakers to allocate the money before the legislative session ends in June. The appeal was the latest move in the longstanding lawsuit, after a lower court ruled that Albany was shortchanging city schools by at least $4.7 billion a year.)

Mayor Michael R. Bloomberg, whose office has presented statistics showing that class sizes have shrunk slightly since 2002, opposed the idea of a referendum last year; the city's Corporation Council issued a ruling that kept such a referendum off the ballot last November. Education advocates have filed a lawsuit challenging the ruling in State Supreme Court in Manhattan and are awaiting a judgment.

"So, speaking for our union, if we are not successful putting this to the voters, we will take the fight to Albany, to the bargaining table, and wherever else it leads us," Ms. Weingarten told the crowd.

Mr. McCourt, the author of "Teacher Man" and "Angela's Ashes" and now the honorary chairman of New Yorkers for Smaller Classes, lightened the mood after Ms. Weingarten's 40-minute address with a speech that poked fun at education officials and politicians, although many had left the ballroom by then.