Organizers of Nelson Mandela's 12-day U.S. visit that is to start June 20 said yesterday that they have been struggling for weeks to balance a public yearning to shake the South African black leader's hand with a desire to spare the 71-year-old's strength.

As a "tentative" schedule for the U.S. leg of his grueling 13-nation trip was released, Mandela canceled an event in Geneva yesterday and returned to his hotel to rest.

Shortly afterward, Mandela resumed his schedule and said, "I feel on top of the world. . . . I am well."

However, the cancellation in Geneva served notice to many of his supporters that Mandela may be overbooked on his six-week tour designed to persuade world leaders to maintain sanctions against South Africa until the system of apartheid has ended.

Mandela, released Feb. 11 after 27 years in prison, began his tour Monday, a day after he was released from a South African hospital. Doctors removed what they said was a benign cyst from his bladder, and the physician who performed the operation said Mandela, who turns 72 July 18, is biologically "a man of about 50."

Still, organizers in Europe and the United States have decided to make certain that everyone expecting a visit from Mandela knows that he might bow out at the last minute.

"We have labeled everything as tentative," said Roger Wilkins, a professor of history at George Mason University and U.S. coordinator for the visit. "It is apt to be changed because of health reasons or security reasons or logistical reasons."

Wilkins said hundreds of groups and individuals have begged to have Mandela stop by their churches, drug-rehabilitation centers or political offices.

Wilkins said he was chosen to head the U.S. welcoming committee because "I was the one who spoke up most vociferously to protect his health and to regard him as a precious 71-year-old human being rather than an ambulatory prize to help Americans feel good about themselves."

Although Mandela and some of those accompanying him said he was feeling fine yesterday, U.N. sources told reporters that Mandela would be taken to a secret location near Geneva to rest this weekend.

Mandela is to arrive in New York June 20 and visit Boston, Washington, Atlanta, Miami, Detroit, Los Angeles and Oakland before flying home July 1.

Among his scheduled events in New York are a lunchtime ticker-tape parade in Manhattan, a motorcade through Harlem, a rally at Yankee Stadium, breakfast with business leaders and an address to the U.N. General Assembly.

In Boston, he is to attend a rally and lunch with "prominent Americans and members of the Kennedy family."

Mandela's three days here are to include meetings with black leaders June 24 and with President Bush and Secretary of State James A. Baker III the next day.

His third day here appears to be one of the longest in his U.S. visit. It is to start with a Congressional Black Caucus breakfast at 8 a.m., followed by a speech to a joint session of Congress at 11, afternoon talks with congressional leaders and a rally at the D.C. Convention Center at 7 p.m.

In Atlanta the next day, Mandela is to lay a wreath at the grave of the Rev. Martin Luther King Jr., attend an afternoon convocation at Morehouse College and an evening rally at Grant Field, the stadium at Georgia Tech.

On June 28, he is to deliver a morning speech to a union convention in Miami, visit an automobile-assembly plant in Detroit and appear at an evening rally at Tiger Stadium there.

On June 29, Mandela is to fly to Los Angeles for a rally at the Hollywood Coliseum, and he is appear the next day for a rally at Oakland-Alameda County Stadium.

Mandela also is expected to talk to news organizations and participate in television interviews during his visit.

Decisions on Mandela's schedule were being made by an ad hoc group of black leaders formed in May as the Nelson Mandela Welcome Committee. The group's executive committee, making decisions on his schedule, included Lindiwe Mabuza, chief representative of the African National Congress to the United States; Randall Robinson, executive director of TransAfrica; Harry Belafonte, and Wilkins.

Security is being provided by the State Department and, by late yesterday, about 3,000 journalists had requested credentials to cover the visit.

MANDELA'S TENTATIVE U.S. SCHEDULE

JUNE 20, NEW YORK

Early morning arrival at John F. Kennedy International Airport. Official welcoming ceremony.

Lunchtime ticker-tape parade in downtown Manhattan, ending at City Hall reception.

Evening meeting with South African exile community.

JUNE 21, NEW YORK

Morning ecumenical service at Riverside Church.

Evening motorcade in Harlem, rally at the Harlem State Office Building, meeting with black journalists.

Evening rally at Yankee Stadium.

JUNE 22, NEW YORK

Breakfast with business and financial community.

Morning address to the U.N. General Assembly, followed by news conference.

Evening private meetings with anti-apartheid activists.

JUNE 23, BOSTON

Morning community meeting with students at Madison Park High School.

Lunch at John F. Kennedy Library with prominent Americans, including members of the Kennedy family.

Midday public rally at the Esplanade.

JUNE 24, WASHINGTON

Briefings and meetings with members of the African National Congress, the South African exile community and the African diplomatic corps.

JUNE 25, WASHINGTON

11 a.m., meeting with President Bush.

4 p.m., meeting with Secretary of State James A. Baker III.

5:40 p.m., meeting with AFL-CIO executive council.

JUNE 26, WASHINGTON

8 a.m., breakfast with Congressional Black Caucus.

11 a.m., speech to joint session of Congress.

Afternoon meetings with congressional leaders.

7 p.m., rally at D.C. Convention Center.

JUNE 27, ATLANTA

Morning welcome at airport.

Morning wreath-laying ceremony at grave of the Rev. Martin Luther King Jr., followed by a civil rights tribute.

Afternoon convocation at Morehouse College, with presentation of honorary degrees from predominantly black colleges and universities.

Evening rally at Grant Field stadium.

JUNE 28, MIAMI and DETROIT

Morning speech to convention of the American Federation of State, County and Municipal Employees at Miami Beach convention center.

About 3 p.m., arrival in Detroit.

Afternoon visit to Ford River Rouge assembly plant.

Evening rally at Tiger Stadium.

JUNE 29, DETROIT and LOS ANGELES

Breakfast with midwestern South African community.

Late morning (PDT) arrival at Los Angeles International Airport, with welcoming ceremony and reception at City Hall.

Evening rally and concert at Hollywood Coliseum.

JUNE 30, OAKLAND

Late morning welcome at airport.

1 p.m., rally at Oakland-Alameda County Stadium.

Afternoon private meeting with South African community.

7 p.m., reception.

JULY 1

Departure.