Hundreds of thousands of cheering New Yorkers filled sidewalks, clung to lampposts and flung hundreds of tons of confetti from windows as the freed South African activist sped along lower Broadway, shielded by a bulletproof enclosure on the back of a flatbed truck.

"It's a great moment not only for blacks but for people of every race and creed," said Patricia Comas, a Barclay's Bank officer who spent several hours waiting in a dense crowd for Mandela to pass by Wall Street and Broadway. "It's a great day for lovers of freedom."

Mandela's arrival in New York is partly a celebration of his liberation on Feb. 11 - after more than 27 years in prison - and partly a reminder to supporters that the struggle to end apartheid is incomplete.

"Apartheid is doomed," Mandela said to cheers at City Hall, where he received the key to New York City from Mayor David N. Dinkins. "South Africa shall be free. The struggle continues."

Mandela urged the U.S. government to maintain economic sanctions on the South African government, a theme he has sounded repeatedly since he began his six-week, 13-nation tour.

"Our simple message, in all these countries, is that the sanctions should be maintained," Mandela said at Kennedy International Airport, where he arrived more than two hours late from Montreal, the last city in a three-day tour of Canada.

Mandela is scheduled to spend three days in New York, where he will address the United Nations General Assembly tomorrow. Then he will travel to Boston and Washington, where he is scheduled to meet with President Bush on Monday and to address a joint session of Congress on Tuesday.

Bush said yesterday that he would tell Mandela that sanctions would not be lifted until certain conditions under U.S. law were met. Bush said that his earlier reservations about sanctions might have been misguided, because the sanctions may have nudged democracy along.

Mandela also is to visit Atlanta, Miami, Detroit, Los Angeles and Oakland, Calif., before leaving the United States on July 1.

Mandela beamed broadly and waved to crowds as his motorcade whisked him and his wife, Winnie, from the airport to a brief stop at a predominantly black high school in Brooklyn, where students chanted, "Keep the pressure on."

"It was the single most memorable thing I've ever witnessed," said Gov. Mario Cuomo, referring to the reactions of bystanders yesterday.

At times Mandela appeared drawn and fatigued. Several meetings and a dinner party Mandela was to have attended last night were canceled because he was tiring, officials said.

Tour organizers expressed concern that the worldwide tour was taking its toll on the 71-year-old and said his schedule could be abbreviated. Last month, he underwent minor bladder surgery.

One purpose of the tour is to raise millions of dollars for the African National Congress, the anti-apartheid organization that was legalized in February after being banned for 30 years. Mandela is deputy president of the ANC.

Organizers in each of the cities had to commit themselves to raising a minimum of $1 million. So Mandela's schedule is filled with private and public fund-raising events, including a rally tonight at Yankee Stadium.

Tour organizers said they were besieged with requests from politicians, organizations and entertainers seeking to bask in the aura of the legendary leader.

Dinkins appeared likely to gain personal prestige by the presence of a man he called yesterday an "international symbol of freedom." The Mandelas will stay at the mayor's home, Gracie Mansion, during their three days in New York.

Dinkins also pitched tickets to the Yankee Stadium rally on radio advertisements, saying, "Come make history with us." Organizers said yesterday they had sold all but 10,000 of the 50,000 tickets to the rally.

Perhaps the most electrifying public event was Mandela's triumphant drive down New York's "Canyon of Heroes" while paper rained down from skyscrapers.

Ticker tape - 150 miles imported from Connecticut, as well as paper towels, toilet paper, adding-machine tape, computer cards, envelopes, clumps of shredded documents and loose-leaf notepaper of all colors - fluttered in the breeze above Broadway, catching on trees and in the 40-foot antennas that protrude like masts from the top of television news trucks.

More than 50 organizations representing almost every ethnic group in New York preceded Mandela up Broadway - bagpipe corps, scout troops, school bands, labor groups, African Americans, Asian Americans, Arab Americans and a Korean cymbal-and-drum corps wearing "Free South Africa" headbands.

Security for the parade was tight. Uniformed sharpshooters were posted along the route and the city assigned 12,000 police officers to control the crowds.

Mandela waited to proceed along the parade route until all of the marchers ahead of him had completed the parade and Broadway was clear. Then he sped along the route in an 8-foot-long glass-and-steel shed on the back of a truck. The vehicle, dubbed the Mandela-mobile by the police, was built by the Federal Bureau of Diplomatic Security.

Mandela's visit meant different things to different people. But most black Americans said they identified with Mandela's struggle and were inspired by his quiet persistence.

"He's a wonderful person to survive 27 years in prison without animosity," said Vernez Becks, a retired IRS auditor who came on an early train from Freeport, Long Island, to stake out a curbside location.