The United States agreed yesterday to provide $3 billion in new military aid to Israel and to speed up delivery of advanced F16 fighter-bombers there as part of the U.S. contribution to the Middle East peace settlement.

The $3 billion, slightly more than the $2.5 billion in aid mentioned earlier by U.S. officials, will help pay the costs of Israel's military withdrawal drawal from the Sinai Pninsula and the construction of two air bases in the Negev region.

The agreement was announced at the Pentagon by an ebullient and beaming Israeli defense minister, Ezer Weizman, who declared: "If all goes well, there will be a celebration Monday on the signing of the treaty."

However, before returning to Israel last night he was not able to clear up the final details of a military withdrawal agreement with Egypt.

Agreement on the timing of Israel's stage-by-stage lullback from its strategic Sina positions will be necessary before a peace threaty can be completed

In what some U.S. officials described as a softening position, Israel has offered to evacuate its military base at El Arish three months after the treaty signing and to vacate the Sinai oil fields after a nine-month delay, Weizman said.

Informed U.S. officials said there was no indication that the talks had run into a serious snag, but they said the two sides were still "chipping away at the issues." Pentagon officials said they were "hopeful" that the details of the phased withdrawal would be worked out quickly.

After paying what he called an "au revoir" call on Egyptian Defense Minister Kamal Hassan Ali and his team at the Madison Hotel, Weizman left two Israeli aides behind to continue the talks.

An indication of the heated pace of events surrounding the peace initiatives is the fact that Israeli Foreign Minister Moshe Dayan is due to arrive here Thursday to work out a memorandum of understanding on U.S. security assurances for Israel.

Officials said that, barring unforeseen complications, Israeli Prime Minster Menachem Begin could fly here as early as Friday to prepare for a treaty signing next week.

The $3 billion aid package to Israel will cover a three-year period and be in the form of $300 million in new grants and $2.2 billion in loans. This is in addition to the $1.8 billion in annual U.S. military aid and other assistance that goes to Israel now.

The United States also agreed to begin delivery of 75 F16 jet fighter-bombers early next year, instead of in late 1981 as origunablly planned.

Defense Department officials said they could not give details now on the type and quantity of other military equipment the United States has agreed to supply Israel.

The Pentagon also has agreed to let Israeli firms bid on U.S. defense contracts.

As the Carter administration was completing its aid package with Israel yesterday it also was opening a new chapter in Middle East history by agreeing to become a major arms supplier to Egypt.

The pledge to consider a lengthy Egyptian military shopping list was given by Defense Secretary Harold Brown when he met with Defense Minister Ali yesterday.

In a breakfast meeting with reporters prior to that, All indicated that Egypt sought advanced aircraft, ships and the Hawk antiaircratt system. Defense Department officials said assurances had been given that the United States would consider providing Egypt aircraft more advanced than the F5, though not necessarily the F16.

Submarines and tanks also were discussed with the Egyptian delegation. Defense Department officials said an aid figure of "less than $3 billion" was likely.

Cairo officials have told Americans that the threat requiring a modernization of Egyptian armaments comes not from Israel but from Libya, Ethiopia and the Sudan. At his breakfast meeting with reporters. All spoke of the threat of "big power" activity in Ethiopia and Yemen, and indicated he meant the Soviet Union.

Until now, Saudi Arabia has been Egypt's principal source of aid funds, providing $1.5 billion a year. Ali said Egypt and the United States understood that progress on the Palestinian issue will decide whether this aid continues after a peace agreement.

National security affairs adviser Zbigniew Brzezinski returned to Washington late yesterday saying only that he was "encouraged" by his talks in Saudi Arabia and Jordan, which are withholding support of the peace initiative.