In a historic moment, the men who have led the United States since 1969--Presidents Nixon, Ford, Carter and Reagan--met at the White House yesterday, brought together by the murder of Egyptian President Anwar Sadat, who had been a key player in the Middle East policy of all four.

The visitors arrived as presidents do, settling onto the South Lawn in a Marine helicopter. Nixon, Ford and Carter had done it as president, but now they were riding together and President Reagan was standing at the end of a red carpet with Nancy Reagan to greet them.

The lawn at dusk was brightly lit by floodlights as Carter, his wife, Rosalynn, Ford and Nixon descended the steps from the helicopter.

A crowd of several hundred White House staff members broke into applause as soon as Carter appeared, and the applause, mixed with whistling, grew louder as each former president appeared and waved.

The Carters held hands as they walked four abreast with Ford and Nixon toward the waiting Reagans. All of them wore serious expressions; Nixon was deeply tanned.

Reagan shook hands first with Nixon, who then kissed Nancy Reagan on the cheek. After the complete round of handshaking, the four presidents walked inside the White House for a brief talk, cocktails and hors d'oeuvre in the Blue Room.

Never before in this century have four presidents gathered together. During President Kennedy's administration, former presidents Hoover, Truman and Eisenhower were alive, and there were briefer periods in the presidencies of Lyndon B. Johnson and of Nixon when three of their predecessors were alive.

Carter, Ford and Nixon were invited to the White House on short notice yesterday and came within an hour before they left Andrews Air Force Base for Cairo as part of the U.S. delegation to Sadat's funeral.

Carter returned to the White House for the first time since he lost it to Reagan. Nixon was returning for only the second time since Aug. 9, 1974 when, as the only president driven from office by scandal, he took a helicopter from the South Lawn to private life.

At Carter's invitation, Nixon had attended a state dinner honoring Chinese leader Deng Xiao-ping. Ford visited Carter in the White House several times and had visited Reagan there once.

White House officials said the four presidents and Vice President Bush stood in a circle and discussed the Middle East and Sadat for most of their time together.

When the group returned to the South Lawn, Reagan read a statement praising Sadat as "a man of peace in a time of violence." He told those who "choose violence over brotherhood" that they had feared Sadat alive, "but in death you must fear him more, for the memory of this great and good man shall vanquish you."

Reagan thanked the former presidents for representing the United States at the funeral and ended with one of his favorite Irish expressions: "Until we meet again, may God hold you in the hollow of his hand."

After a farewell handshake with each of them, the Reagans escorted the visitors to the helicopter. Carter broke away for a moment, walking to the crowd of reporters to shake hands. "I'm glad to be going, but it's a sad occasion," Carter said.

When the four reached the short flight of steps at the helicopter, they reassembled according to protocol. Carter turned for a brief wave from the top of the stairs and entered the helicopter ahead of his wife. Ford started to look around at the applauding crowd, then stooped to enter without stopping.

Nixon did not hesitate. He mounted the steps briskly, looking straight ahead, and in seconds the door was closed behind him.

The Reagans waved a last time, then retreated from the propeller wash and walked back into the White House. The White House visit had lasted about 35 minutes.