The United States is not abandoning the search for peace in the Middle East, but sees little likelihood of forward movement until "absolutely fundamental" differences with Israel are resolved, Secretary of State Cyrus R. Vance said yesterday.

In a news conference centering on the unsuccessful White House talks between the two nations this week, Vance set out more clearly than ever the major disagreements between President Carter and Prime Minister Menachem Begin and gave some details of U.S. suggestions offered to the Israeli leader.

"Let me make it crystal clear that we have not given up hope," said Vance, citing the willingness of both Egypt and Israel to continue the peace process.

However, he said that a resumption of direct Egyptian-Israeli negotiations in the near future "is unlikely," and said the momentum toward agreement has been "clearly much slowed down by the recent events."

Vance, who is nearly always officially optimistic and who usually avoids strong language, went out of his way to make clear the basic disagreements which caused the deadlock in the Carter-Begin talks:

Israeli withdrawal from te occupied West Bank and Gaza strip in keeping with U.N. Security Council Resolution 242, the territory-for-peace bargain which has been "the basis of negotiations between the parties for many years."

The Begin government has argued that Israel is not compelled to withdraw from any part of the West Bank as part of an overall peace agreement. The United States argues that negotiated withdrawal from areas of the West Bank as well as the Sinai and Golan fronts is a vital part of any comprehensive peace agreement.

"In our judgment it is clear from the past history - and from the conduct of the parties that 242 does, indeed, apply on all fronts," Vance said. Calling this "absolutely fundamental," he said there are "very substantial obstacles ahead" unless this differencce of interpretation can be resolved.

Israeli settlements in the Sinai as well as the West Bank, another matter of "fundamental difference between the parties" and "a substaintial obstacle to any progress."

"It was very clear" that Begin will not agree to give up settlements in the Sinai as part of a peace with Egypt or let the Israeli settlers be under Egypt's protection, Vance said.

Egyptian President Anwar Sadat has rejected Israeli enclaves in Egyptian territory on a permanent basis. Begin has said the settlements are necessary to block infiltration and gun-running into the Gaza strip.

The United States and Israel are also at loggerheads over Jewish settlements in the West Bank. The United States argues that creating such enclaves in an area under military occupation is contrary to international law and that they create obstacles to ultimate Israeli withdrawal. Israel under Begin argues that the West Bank was never sovereign Arab territory and that Jews have "a perfect right" to settle there.

U.S. ideas of an "interim agreement" for a limited Palestinian self-determination on the West Bank. The proposals, Vance confirmed, envision a choice for West Bank Palestinians after a period of a few years to affiliate with Israel, affiliate with Jordan or continue the "interim" arrangement which would be worked out for the time being. In this plan, an independent Palestinian state would not be among the choices offered.

Israel has rejected this proposal on grounds that it might lead in time to a Palestinian state threatening Israel. U.S. officials say that Sadat and possibly King Hussein of Jordon would accept it if the details are satisfactory.

Vance suggested, and other U.S. officials said more explicity, that the next major development to be watched is the Israeli reaction to the failure of Begin's talks here this week. U.S. officials by signs of a major debate in Israel about Begin's policies.

Another front being closely watched is the reaction of Sadat to the out-come of the Carter-Begin talks. White House sources said Carter sent a written message to Sadat yesterday covering his discussions with the Israeli leader. U.S. officials expressed hope that Sedat will recognize the need to allow time for Israel to debate its peace positions.

Vance declined comment on Israeli political developments yesterday, saying "it would be totally improper for us to interfere affairs. He denounced as "totally false" reports that the Carter administration is trying to force Begin out of office to break the stalemate on peace issues.

Replying to charges by Begin, Vance said the United States has not changed is position on his proposal for "self-rule" in the West Bank and Gaza Strip. Vance said the Carter administration had welcomed it last December as "as constructive step," but "we did not endorse the proposal."

In a related matter, Vance defended the proposal U.S. sale of F15 jet war-planes to Saudi Arabia , denying the Israel, charge that the planes would make Saudi Arabia a confrontation state in a future Arab-Israeli war.

On other subjects, Vance told his news conference that U.S. relations with the Soviet Union are "at a delicate stage" in which there has been retrogression in some areas and progress in others. He said two or three "very tough" items remain in the strategic arms negotiations, but said there was no time limit set on reaching agreement.