The two grand marshals of the city’s annual gay pride parade are criticizing Mayor Bloomberg for joining the march below St. Patrick’s Cathedral.

Mr. Bloomberg, who has said he favors same-sex marriage, joined yesterday’s parade down Fifth Avenue at 48th Street, two blocks south of the cathedral.

Mr. Bloomberg has started walking in the parade below the cathedral every year, continuing the precedent established by Mayors Koch and Giuliani before him. Yesterday, he marched alongside the speaker of the City Council, Christine Quinn, the first openly gay leader of the council. Ms. Quinn started the parade at the beginning of the route on 52nd Street.

Rabbi Sharon Kleinbaum and the Reverend Troy Perry, the parade’s two grand marshals, criticized Mr. Bloomberg for not walking past the cathedral, which has during past parades been the site of protests of the Catholic church’s position on homosexuality and of counterprotests directed at the parade.

“Shame on you, Mr. Bloomberg,” Ms. Kleinbaum said at a news conference when asked about the mayor’s decision to start the march below the church. “We expect you to be at the head of this march.”

Rev. Perry said: “I think the mayor’s making a mistake if he’s going to run for president.”

A spokesman for Mr. Bloomberg, Stuart Loeser, said the mayor has always started on the corner of 48th Street. While he did not specify why, the issue is not a new one for elected officials.

In 2002, the New York Times reported that Mr. Bloomberg had tentatively planned to start the parade where it begins at 52nd Street, but that he changed his plan at the last minute.

“The mayor wants to avoid some of the disrespectful acts that have taken place near St. Patrick’s Cathedral during the past parades,” the mayor’s former press secretary and current deputy mayor, Edward Skyler, told The New York Times at the time.

This year’s gay pride parade comes less than a week after the state Assembly passed a bill to legalize same-sex marriage. It also comes during a frenzy of speculation about whether Mr. Bloomberg, who last week resigned from the Republican Party, is going to run for president. Mr. Bloomberg’s administration has argued against same-sex couples in court, saying that current law does not allow gay marriage. But he has also said he wants that law changed so that gay couples can legally wed.

A professor of public affairs at Baruch College, Douglas Muzzio, said Mr. Bloomberg was simply following tradition and that it didn’t make sense for him to insult the church or Cardinal Egan.

“The guy is marching in the parade, he’s waving the flag, he’s demonstrating his public support of gay rights, and yet he’s being criticized for not sticking it to the cardinal,” Mr. Muzzio said.

He said those criticizing the mayor are “violating the rule of not letting the perfect veto the good.”

While the Catholic Church has maintained its opposition to homosexual sex, Ms. Kleinbaum and Rev. Perry both emphasized the need for religious leaders to embrace the gay community.

“We stand here because we reject the idea that religion can be used as a tool against us and our community,” Ms. Kleinbaum said. “Those who use religion to pursue an anti-gay agenda are, I believe, blaspheming God’s name.”

The parade drew many colorfully and scantily dressed participants, with g-strings and feathered costumes abounding.

Gospel singers from the Rehoboth Temple in Harlem belted “This is the day the Lord has made,” while marchers and spectators sported stickers that said “God made me queer.”

In addition to Mr. Bloomberg and Ms. Quinn, many other elected officials, including Senator Schumer, participated in the march.