Carter administration officials acknowledged yesterday the high risks involved in tonight's meeting in Jerusalem between Egyptian President Anwar Sadat and Israeli President Menahem Begin but insisted that the potential rewards outweigh the inherent dangers.

President Carter called Sadat yesterday morning to wish him success and later told reporters that the Egyptian leader is "excited enthusiastic and confident" about his impending visit to Israel.

The telephone call came at the start of a day that was dominated by foreign policy issues, particularly the rapid developing events in the Middle East.

In the afternoon, Carter met with Soviet Ambassador Anatoly F. Dobrynin, who gave him a personal message from Soviet President Leonid I. Brezhnev.

The contents of the message were not disclosed. During the 15-minute meeting, Dobrynin told reporters, he and the President did discuss the Middle East, although not specifically the Sadat-Begin meeting.

Officials said later that the Brezhnev message was not prompted by developments in the Middle East but was a reply to a personal message the President had sent to Brezhnev earlier this month on the 60th anniversary of the Russian revolution. The Carter letter had dealt with arms limitation talks, among other topics, the officials said.

During the day, however, the focus of most questions was the dangers posed for an overall peace settlement in the Middle East by the Sadat mission and already angry reaction to Sadat's hold move in some parts of the Arab world.

Privately, one presidential aide conceded that the biggest fear in the White House was that Sadat visit will be viewed as an attempt by Egypt to reach a separate peace with Israel, leading to "a situation in which the Arab world becomes split, partially immobilized and intransigient."

Such a development would almost certainly doom the administration's policy of seeking a Geneva conference to negotiate a comprehensive peace settlement among israel and all of her Arab neighbors.

The double-edged aspects of Sadat's visit to Israel were also mentioned yesterday by Secretary of State Cyrus R. Vance, "We can only hope and pray that it [the Sadat visit] will contribute to peace in the Middle East, realizing at the same time that it is a very high risk proposition fraught with danger."

Baroody said Vance indicated during the meeting that he, too, was "extremely hopeful and yet nervous at the same time."

But in a sign of the divisions the Sadat-Begin meeting has caused in the Arab world, Professor Edward Said, a Palestinian-American who teaches at Columbia University, called the Sadat mission "so theatrical" and said it has "increased divisiveness in the Arab world."

Vance, according to Said, told the delegation that despite the risks involved the Sadat visit is important enough to deserve support from the United States and others.

Zbigniew Brzezinski, the White House national security adviser, termed the Sadat visit to Israel "an historic breakthrough"

"It is a gesture of peace that is probably unparalleled in contemporary history," Brezezinski told reporters outside the White House. "So it's terribly important that it succeed. We all know the risks. But without risks, sometimes there aren't great accomplishments."

Brezezinski predicted that if Sadat's initiative "has the earmarks of success, my guess is there will be more and more support for what he had done and the recognition that this is in the interest of all, including and above all the Arab nations.

Shortly after Brezezinski re-entered the White House, Israel Ambassador Simcha Dinitz emerged following a one-hour lunch there with Vice President Mondale, White House counsel Robert Lipshutz and Hamilton Jordannn, the President's chief political adviser.

Dinitz said the Sadat-Begin meeting is "a psychological breakthrough that hopefully will lead to a political breakthrough."

On the question of risks. Dinitz said. "There is no move that can take place without risks. The risks are that neither side will get as much as they expect."

But, he added, the Israeli government "will do everything in our power to make it an important step."

The comings and goings on the driveway outside the entrance to the West Wing of the White House underscored the suddenly accelerated pace of developments in the Middle East.

Earlier in the day, White House officials released the text of a message from Begin that was delivered to Carter Thursday night by Dinitz.

In the message, Begin said he hoped "that this dialogue [with Sadat] will continue" and toooold the President that "without your contribution these events could not and would not havve been set in motion."

In his 10-minute telephone conversation with Sadat, Carter told the Egyptian leader. "The eyes of the world are on you."

Israeli sources said that contrary to published reports, the Carter administration has made no suggestions to Begin for his talks with Sadat.

It would be "completely superfluous" for the United States to offer suggestions to Israel on handling Arab issues, these sources said, in light of Israel's years of experience with the Arabs.

There is, however, increasing discussion between Israel and the United States about the Sadat visit because Begin wants to keep Carter well informed of development, the sources said.