"I have spent a great deal of my time in prison writing to the heads of the religious organizations in all countries because of the key role which they are playing in the struggle," Mandela said.
The 71-year-old deputy president of the once-banned African National Congress was presented $200,000 for the ANC after his address.
Mandela's 12-day U.S. tour is part of a 13-nation trip to urge the world to keep up pressure against his homeland until all traces of apartheid, South Africa's system of racial segregation, are gone.
"Apartheid is doomed. South Africa shall be free. The struggle continues," Mandela said yesterday after he arrived in New York to an outpouring of love and a hero's ticker-tape parade up Broadway.
His second day in New York started with a breakfast-hour stroll that got his security team hopping.
About a dozen security men surrounded Mandela and police in the blocked-off streets outside Gracie Mansion, the mayor's official residence, where Mandela and his wife, Winnie, are staying.
"It was very nice," Mandela said afterward. "Thank you. I'm sorry. I didn't think it would be so much trouble."
"I am feeling on top of the world," he said at a brief photo session with the Rev. Jesse Jackson.
The photo session was in lieu of a scheduled breakfast, one of a number of Mandela events that have been canceled or truncated so far in the tour.
Asked about why his schedule was undergoing constant change, he laughed and said he had "ideas of my own."
But the schedule-juggling was said to indicate the concern of trip organizers over the health of the 71-year-old fighter against apartheid.
They said yesterday that Mandela's U.S. schedule, which calls for 34 major events during an eight-city, 12-day tour, may be pared back.
"We're playing it by ear," said Sylvia Hill, associate coordinator of the national welcoming committee.
A benign cyst was removed from Mandela's bladder three weeks ago. Previous stops on his world tour have been nowhere near as grueling as the American leg is scheduled to be.
Organizers canceled a meeting late yesterday with South African exiles and Mandela spent a quiet, private evening with Mayor David Dinkins and a few invited guests at Gracie Mansion.
Mandela appeared tired and worn as he stepped off the plane at Kennedy International Airport around noon yesterday.
But he seemed to gain strength during a day of crowd-pleasing motorcades and speeches, although several private events were canceled to provide extra rest time.
Mandela got his message out at the airport, saying economic sanctions against the white government of South Africa must be maintained.
"It is no use to demand that apartheid is scrapped," he said. "What brings about changes in politics is the type of action which you are prepared to embark upon in order to bring about those changes."
President Bush, who meets with Mandela next week, reiterated yesterday that the United States would not lift its sanctions until South Africa meets the requirements of the sanctions law. Those requirements include the release of all political prisoners there.
Mandela was met at the airport by a VIP welcome crew that included Jackson, Govs. Mario Cuomo of New York and Jim Florio of New Jersey, singer Harry Belafonte, ANC representative Lindiwe Mabuza and diplomats from more than 100 countries.
These celebrities, who had tasted glory as athletes, entertainers or politicians, admitted that they stood in awe of Mandela.
Tennis star Arthur Ashe, a longtime activist against apartheid, called Mandela's first visit to the United States "a tremendous day . . . especially since I had always believed he would die in jail."
Mandela was released on Feb. 11 after spending more than 27 years in South African prisons.
Political activist Dick Gregory also expressed joy - and disbelief.
"When he walked out of jail, you could feel the vibrations all over the planet," Gregory said. "He could have walked out full of anger, hurt and bitterness. Instead, he walked out with love, dignity, integrity, and touched the God spirit in the heart of each of us."
Mandela went ahead with a visit to Boys and Girls High School in Brooklyn, despite running hours late.
A press aide said Mandela refused to disappoint "the children" and went
from the airport to the school, to be met by an estimated 10,000 to 20,000 people, many waving the ANC flag and banners that said "Free South Africa."
Then came a massive parade through lower Manhattan's "Canyon of Heroes," and ceremonies at City Hall with Dinkins. Police estimated that 350,000 people lined streets along Mandela's route from the airport, and another 450,000 turned out for the ticker-tape parade along Broadway to City Hall.
Mandela waved and smiled to people who lined the streets, 10 deep at some points. They all wanted a glimpse of the man who had, for at least one day, brought them together in a spirit of unity and awe.
Irish, Arabs, Italians, Ethiopians, Chinese, Koreans and African-Americans were represented in the parade, and even more heritages in the crowds that often threatened to surge across the barriers of police and wooden barricades that separated them from Mandela.
But despite the gridlock alerts, the traffic detours and the throngs of people, several police officers who had handled other such parades for presidents and astronauts said they had never seen a more orderly or united group of people.
Mandela, they said, had managed to do something they had never seen before - inspire people in an extremely diverse city to look at others as just people.
"I've seen people crying and shouting, but never anything like this," said Cuomo. "It was the single most memorable thing I've ever witnessed."