The Middle East peace summit at Camp David, which the White House described yesterday as being in its "final stages," has moved beyond the threat of a total breakdown within the past 24 hours, according to informed sources.

More limited but significant optimism was expressed publicly by Israeli press spokesman Dan Pattir, who told Israel radio that while there may have been cause of pessimism last week, "in the meantime things have changed, and the pessimism reported in the Egyptian press is exaggerated."

In a day of nearly nonstop negotiations and contacts by the United States, Egyptian and Israeli delegations, White House press secretary Jody Powell told reporters that the new "intensity and specificity" of the discussions suggested that the conference has reached its "final stages."

But Powell again declined to give any clear indication of the outcome of the summit or its finishing date. He repeated warnings that "uncertainties abound" and said there was no basis for informed speculation on the outcome.

But the impression that Carter had achieved enough in the way of a broadly worded statement that both Egypt's Anwar Sadat and Israel's Menachem Begin could agree to was bolstered by his decision to stay at Camp David last night and work rather than host a White House reception for stock car racers that featured a concert by one of Carter's favorite singers, Willie Nelson.

Late yesterday, White House officials announced that Carter was also postponing for one week political appearances in the Carolinas, Pennsylvania and Ohio that he had been scheduled to make tomorrow and Saturday.

There were no announced meetings involving Carters, Begin or Sadat yesterday. Carter met with the Israeli leader for 80 minutes Tuesday night, Powell said, and then went into a late-night session with Secretary of State Cyrus R. Vance, his national security affairs adviser, Zbigniew Brzezinski, and other U.S. officials.

The president reassembled his advisers at 6:45 a.m. yesterday for another session that reportedly involved a serious drafting effort.

According to one report, there was also a key three-way meeting yesterday involving Israeli Foreign Minister Moshe Dayan, Sadat's minister for presidential affairs, Hassan Tuemi, and an unnamed U.S. official.

There was no official confirmation of the report, but diplomatic analysts said such a meeting would be a necessary preliminary to the final drafting of a compromise formula that could be accepted by the three leaders in a joint meeting. They have not held a trilateral session since last Thursday.

A new tone of optimism entered comment on the talks after Begin returned from his meeting with Carter in good spirits Tuesday night. Carter had met earlier in the day with Sadat, and according to one source, appears to be gaining ground in an effort to convince the two leaders to accept an ambiguously worded "framework" that will allow direct Egyptian-Israeli talks to continue and express new Israeli flexibility on withdrawal on the West Bank of the Jordan River.

The source cautioned that last-minute reversals could still bring failure at the summit, but said that was not a strong probability now. But details of what Carter is actually proposing to Sadat and Begin remained eclipsed behind a nearly total news blackout decreed by Carter.