The United States has pledged formal consideration of an increased American presence in the Middle East and new emergency aid for Israel if Egypt violates the peace treaty the two nations signed Monday, U.S. officials said yesterday.

The highly conditional pledge, which implies a greater U.S. security role in the Middle East if the treaty collapses, is contained in a U.S. Israeli "memorandum of understanding" that American and Istraeli negotiators signed Monday afternoon. It is to be released publicly later this week.

Among the possible "economic, political and military" steps that the United States would consider taking to protect Israel are naval action to break a sea blockade and emergency military resupply efforts similar to the arms airlift during the 1973 Arab-Israeli war, Israeli sources said.

But U.S. officialsexphasized that these and other steps were listed in the memorandum to illustrate the types of action that the United States might consider taking in an exergency and were not specific committments to Israel.

The document reportedly emphasizes that congressional approval would be needed for many of the contingency steps outlined. Determination of when a treaty violation has occurred rests solely with the United States, and the memorandum requires consultation with botn Egypt and Israel before a U.S. review of possible action-starts.

Israel insisted on receiving the new U.S. security assurances and an accompanying memorandum guaranteeing U.S. oil supplies to Israel for 15 years before giving final agreement to the peace treaty, signed Monday by Israeli Prime Minister Menachem Begin and Egyptian President Anwar Sadat and witnessed by President Carter.

State Department spokesman Hodding Carter said yesterday that the United Sates had offered to negotiate a similar memorandum with Egypt, which declined the offer for the time being.

Under the treaty, Israel will return theSinai Peninsula to Egypt in stages over the next three years in return for Egyptian agreement to establish full diplomatic, commercial and clutural relations with the Jewish sate. The memorandum's assurances go beyond the three-year period, U.S. officials said yesterday.

Begin reportedly described the memorandum to Israeli reporters yesterday as "a beautiful docment, well-written, and what it contains is very important." Begin, who late left Washington for New York, reportedly specified that the United States is now committed to increasing its presence and to removing any naval blockade mounted against Israel.

Reacting to these reports, U.S. officials said that the wording of the agreement is much more ambiguous and does not go beyond the commitments already made to Israel in a similar memorandum of agreement worked out by former secretary of state Henry A. Kissinger to support the Sinai II disengagement agreement of 1975.

The new memorandum will state that existing agreements, including the Sinai II memorandum, are still in effect.

A key provision of the 1975 agreement prohibits the United States from direct contact with the Palestine Liberation Orgainzation unless the orgainization recognizes Israel's right to exist.

A commitment in the new memorandum to endeavor to take Israel's economic and military needs into consideration if the treaty is violated also parallels a 1975 commitment, according to U.S. officials, who would not specify how the U.S. "presence" would be increased in such circumstances.

The memorandum was signed by Secretary of State Cyrus R. Vance and Israeli Foreign Minister Moshe Dayan two hours after the treaty signing.Negotiations on the memorandum and on a treaty annex involving continued Israeli access to petroleum from the Sinai oil fields were not completed until early Monday morning.

The oil compromise that cleared the way for the treaty signing lets Israel stay in control of the Sinai fields for sven months more, but does not give Israel any special guarantees about future purchases, which will be handled in a routine commercial way.

The Carter administration does accept two specific military obligations under the treaty. It will continue aerial reconnaissance of the Sinai at the request of Egypt and Israel, and pledges to organize and maintain "An acceptable multinational force" to occupy limited force buffer zones if the U.N. Security Council refuses and is unable to do so.

President Carter's special diplomatic envoy to the Middle East, Alfred L. Atherton Jr., will probably represent the United States next month when negotiations between the three countries over the West Bank and Gaza Strip territories get under way, U.S. officials said.

The talks, which encompass military discussions between Egyptian and Israeli general officers, will alternate between the Sinai coastal town of El Arish and Beersheba, Israel.

In a television interview Monday night, Sadat said the autonomy talks would begin with Gaza. He made the same proposal last gall during negotiations on the peace treaty, but Israel did not accept it. Administration sources said the United Sates would agree to starting with Gaza if West Bank Palestinians did not agree to join the talks immediately, but Israel's attitude was described as ambivalent.