Pro-Israel New Yorkers will gather on Sunday for the annual Israel Day Parade, a celebration of the Jewish state, but for the first time in recent memory the mayor of New York City will not be joining them.

Mayor Zohran Mamdani said again last week that he would not participate in the event, citing his longtime opposition to the Israeli government. Parade organizers said they believed he was the first mayor to skip the parade, but said they did not have complete attendance records dating back to its start in 1964.

“I said on the campaign trail I would not be attending the parade, and I have made my views on the Israeli government abundantly clear,” Mr. Mamdani said on Thursday at a news conference focused on security preparations for the parade, which begins at 11:30 a.m. in Manhattan.

Standing by his side, Police Commissioner Jessica Tisch indicated that she would march as a representative of his administration. She and Mr. Mamdani said security for the annual event would be tighter than ever.

“As the mayor of our city, I take seriously my responsibility to protect the safety and well-being of every New Yorker and every event, regardless of my attendance,” the mayor said.

Ms. Tisch, who is Jewish and has been a longtime supporter of Israel, described the parade as “one of the most joyful days of the year.”

She added: “It is the mayor’s decision not to march, and it is my decision to march proudly.”

The Israel Day Parade has been a staple of New York’s political calendar for decades, and elected officials and political candidates have often viewed it as an easy way to signal support for Israel and solidarity with Jewish New Yorkers.

But that calculus has become more complicated in the years since the deadly Hamas-led attack on Israel on Oct. 7, 2023, which led to a yearslong series of wars across the Middle East, including in Gaza, where fighting has killed more than 70,000 people and destroyed the economy and civilian infrastructure. Israel has also launched offensives in Lebanon, Iran and elsewhere.

The civilian toll of those conflicts has led to a rapid deterioration of public support for Israel in the United States, with 60 percent of Americans and 80 percent of Democrats and Democratic-leaning independents now expressing a negative view of the country, according to the Pew Research Center.

That deepening negativity has also been driven by the findings of a United Nations commission and Israeli and international human rights groups that Israel committed genocide in Gaza, a view adopted by Mr. Mamdani. Israel has repeatedly rejected those claims, as have many of its supporters in the United States.

The parade is taking place this year against a nationwide backdrop of rising antisemitism, including a number of events in New York that have left the city’s Jewish community on edge. In response to those concerns, Ms. Tisch said the city had enacted its most comprehensive security plans ever for the event.

There will be an increased police presence along the parade route, which stretches down Fifth Avenue from 74th Street to 62nd Street, involving plainclothes officers, checkpoints and road closures, Ms. Tisch said.

Parade-watchers will not be permitted to gather on the west side of the route, abutting Central Park, to ensure that all spectators enter through designated screening points.

Mark Treyger, the chief executive of the Jewish Community Relations Council of New York, which organizes the parade, said the theme of this year’s event was “Proud Americans, Proud Zionists.” He declined to share his feelings on Mr. Mamdani’s decision not to attend.

“My focus and my main concern is about those who are showing up and less about those who choose not to,” he said. “At the same time, anyone in elected office or a leadership position has a moral obligation to ensure every single community they serve feels safe, seen, supported and respected.”

Other Jewish leaders were more direct. Jonathan Greenblatt, the chief executive of the Anti-Defamation League, which has been sharply critical of Mr. Mamdani since before he was elected, criticized him as “the first mayor in more than 60 years to turn his back on the world’s largest Jewish community outside of Israel and on friends of the Jewish community.”

He said the parade was “a celebration of Jewish identity, pride and community” and not the Israeli government.

Mr. Mamdani is not the only elected official planning to skip the parade this year. A number of candidates aligned with the Democratic Socialists of America, an organization of which Mr. Mamdani is a part, have said they would not take part in the event.

Brad Lander, a Jewish critic of Israel and a leading Mamdani ally who is running in a Democratic congressional primary, will instead canvass with a progressive Jewish group in Manhattan, his spokeswoman said.

And Representative Ritchie Torres, an outspoken pro-Israel voice in Congress, will skip the parade for the second year in a row because of a scheduling conflict, according to his spokesman.

Several progressive groups allied with the mayor, including Jews for Racial and Economic Justice, Israelis For Peace and the New York City chapter of the multiethnic Israeli group Standing Together, will not participate either.

But many others are planning to march, including Gov. Kathy Hochul; Letitia James, the state attorney general; Thomas P. DiNapoli, the state comptroller; Mark Levine, the city comptroller; and Julie Menin, the City Council speaker.

“We’re not marching in favor of the government; we’re marching in favor of Jewish pride and Jewish identity,” said Ms. Menin, who is Jewish. “I just don’t think a parade should be synonymous with the Israeli government, because it’s not.”

Representative Dan Goldman, the incumbent Jewish congressman that Mr. Lander is seeking to unseat, will also march, a campaign spokesman said. And Eric Adams, Mr. Mamdani’s predecessor as mayor and an avid supporter of Israel, has said he will participate in his capacity as a private citizen.

Israeli elected officials will also join, including Amir Ohana, the speaker of the Knesset, Israel’s parliament, and nearly a dozen other lawmakers, according to a spokesman for the Israeli consulate in New York.

Sally Goldenberg contributed reporting.