President Carter warned Israel and Egypt yesterday that failure to agree on a peace treaty by the Dec. 17 deadline set in the Camp David accords could jeopardize the overall Middle East peace process.

Clearly intending to increase the pressure to break the Egyptian-Israeli negotiating impasse, Carter told a breakfast meeting with reporters that the United States would view the failure to meet the deadline as "a very serious matter."

He did not spell out what actions the United States might take if the deadline were missed, but indicated that if that happened the two parties would be setting a precedent that could begin to unravel the agreements reached during the 13-day Camp David summit conference in September.

"If, because of mutual lack of agreement, we go past Dec. 17, it would cast doubt on whether the Egyptians and Israelis would carry out the difficult terms of the upcoming peace treaty, and it would set a precedent that would have far-reaching, adverse effects," the president said.

Carter's volunteered comments marked his most forceful personal intervention in the Egyptian-Israeli negotiations since the Camp David summit. He said it was his concern over meeting the deadline that persuaded him to dispatch Secretary of State Cyrus R. Vance to Cairo and Jerusalem next week.

The president has used deadlines before to pressure both sides in the complex Middle East peace negotiations. After several days of talks at Camp David, he set Sept. 17 as the final day for negotiations, winning, in the final hours before the deadline was reached, agreements on two "frameworks" for peace in the Middle East.

But while that proved to be a successful negotiating tactic at the summit conference, the question of deadlines and timing is also a central element in the current impasse in the negotiations over one of those "frameworks" governing a peace treaty between Israel and Egypt.

The Camp David accords call for the signing of an Egyptian-Israeli peace treaty and the beginning of negotiations to settle the status of the Israeli-occupied territory of the Gaza Strip and the West Bank of the Jordan River.

The Egyptian-Israeli talks have reached an impasse, in part over Egypt's demand that a peace treaty with Israel include a timetable or target date for setting up autonomous, self-governing units for the West Bank and Gaza Strip Palestinians during a five-year transition period leading to a final settlement of the areas' status.

Israel has rejected this demand as well as a U.S. suggestion that the timetable issue be handled in a letter that would be separate from the peace treaty itself.

Carter clearly intended to warn both Egypt and Israel that failure to meet the initial Dec. 17 deadline -- which is stated as a "goal" in the Camp David accords -- would only further complicate the far more complex negotiations over the West Bank and the Gaza Strip. Chatting informally with reporters following the breakfast, he returned to the same theme.

"I think the 17th date has much more significance than has been recognized because the Camp David accords specifically call for a three-month limitation," he said. "For them to let that date pass and then attribute a great deal of importance to other dates, I think would be a very serious mistake. They would have set a precedent that dates or time limits are not significant."

During the breakfast, the president also repeated his earlier criticism of both sides for "quibbling over what seems to us to be insignificant language differences" and said he would consider the establishment of new Israeli settlements in the West Bank to be a violation of the Camp David agreements.

Later yesterday, Carter delivered the same message about the Dec. 17 deadline to Israeli Ambassador Simcha Dinitz, who paid a farewell visit to him at the White House. Dinitz is leaving his post in Washington to return to Israel Dec. 16.

Outside the White House, Dinitz suggested that he viewed the deadline's importance less seriously than the president. He also asserted that the cause of the impasse "is not Israel."

Meanwhile, in Switzerland yesterday, Israeli Foreign Minister Moshe Dayan denied reports that he plans to meet in Europe with Egyptian Prime Minister Mustafa Khalil.

Dayan also said that another Camp David-type summit conference may be needed to break the deadlock. The Israelis have made similar suggestions in the past, but they have been received coolly in Washington.

On other topics during his breakfast interview by about 30 reporters Carter also:

Gave an optimistic assessment on the strategic arms limitation treaty (SALT) negotiations with the Soviet Union, saying that the remaining differences are "minor" and that "if the Soviets are adequately forthcoming, I would guess that any further delay would be minimal."

Said he had no comment on the fact his brother, Billy, invoked the Fifth Amendment while testifying before a grand jury in Atlanta investigating the financial affairs of former budget director Bert Lance. He said he has never discussed the matter with his brother.

Asserted that South Africa has accepted a United Nations proposal dealing with elections in Namibia, but that he could not discuss details. However, U.N. officials said earlier that the South African response to Secretary-General Kurt Waldheim's plan was not totally acceptable.

Describing his decisions to cut government programs as part of the anti-inflation effort as "a traumatic experience," the president warned that the American standard of living may not rise as rapidly as in the past. quality," he said.