New York Braces for U.N. Pageantry : Celebration: World body’s anniversary draws more than 180 leaders in largest diplomatic gathering in history.

The biggest gathering of world leaders in history--more than 180 presidents, prime ministers and sovereigns--begins in New York today with pageantry, protests and unprecedented security.

An astounding assemblage of dignitaries, including Russian President Boris N. Yeltsin, China’s President Jiang Zemin, President Clinton and such controversial figures as Cuban President Fidel Castro and Palestinian leader Yasser Arafat, are converging on the city for the 50th anniversary of the United Nations.

Mayor Rudolph W. Giuliani will host almost every head of state at a tightly guarded dinner at the World Financial Center in lower Manhattan tonight, kicking off an extraordinary round of celebrations, public meetings and private diplomacy.

“This is the largest diplomatic gathering in the history of the world. . . . The security precautions are also historic in nature,” Giuliani said as the city made final preparations. Midtown streets Friday already were filled with the sounds of sirens from arriving motorcades and grumbling from drivers facing gridlock.

A force of more than 3,000 federal agents backed by thousands more New York City police officers was mobilized to provide security for the events.

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Egypt’s President Hosni Mubarak, who was scheduled to participate, canceled his visit at the last minute. Security personnel said no reason was given, but in 1993 he withdrew from a similarly planned trip to New York to address the world body after Egyptian intelligence learned of an assassination plot against him by followers of radical Sheik Omar Abdel Rahman.

The Egyptian sheik and nine followers were convicted earlier this month in federal court in Manhattan of plotting Mubarak’s death and conspiring to wage a war of urban terrorism against the United States.

Police said almost 60 protests and rallies were planned during the visit of the world leaders. Castro is the primary, but certainly not the only, focus of these demonstrations. Greenpeace, the international organization of environmental activists, announced plans to gather against French nuclear testing in the South Pacific when French President Jacques Chirac speaks before the United Nations.

In a preview of planned larger protests, police said 25 anti-Castro demonstrators gathered near Wall Street on Friday, condemning investment in Cuba.

Giuliani pointedly declined to invite Castro to the dinner he is hosting for other leaders and to a United Nations Day concert on Monday by the New York Philharmonic at Lincoln Center.

“I think New Yorkers should understand the kind of person we’re dealing with here,” the mayor said. “He’s been a dictator for 36 to 37 years responsible for the destruction of an enormous amount of human life, responsible for the destruction of human rights and political rights on a scale that is really reprehensible.”

Arafat will not be dining with the mayor tonight either. He will be feted just across the street from the financial center at a $150-a-plate fund raiser for two hospitals in the Gaza Strip and the West Bank town of Hebron.

With the possible exception of Washington, no city in the United States has the experience and resources to guard such a huge contingent of dignitaries. The police operations orders from the 1960 visit to the United Nations by Castro, Soviet President Nikita S. Khrushchev and 24 other heads of state fill about 200 pages. Over the years, that knowledge has expanded exponentially.

The traffic problems Friday were only a preview of the far greater congestion expected once the commemorative session begins Sunday.

Giuliani asked New Yorkers to be patient and stressed the positives the world body brings to the city.

“The relationship between the United Nations and New York City is a very, very strong one,” the mayor said. “It’s had its rocky moments, but mostly it’s been a very good relationship for both the U.N. and for the city of New York. The U.N. contributes $3.3 billion to the economy of the city.”

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A study by New York City’s Economic Development Corp. shows the United Nations and the diplomatic community to be New York’s third-largest employer. U.N. headquarters alone provides 6,700 direct jobs and $727 million in direct spending, creating a total impact of 12,200 jobs and $1.4 billion in spending, the study said. The headquarters generates $7.1 million in visitor spending.

One of the biggest gripes of New Yorkers is that many diplomats don’t pay parking tickets and are afforded preferential parking spaces in Manhattan. In 1994, unpaid tickets issued to cars with diplomatic license plates totaled almost $10 million.

Times researcher Anna M. Virtue contributed to this report.