The United States advised Israel yesterday that it will veto any effort in the U.N. Security Council to impose sanctions against the Jewish state for its annexation last month of the Golan Heights.

Diplomatic sources said that that assurance was conveyed by Secretary of State Alexander M. Haig Jr. to Israeli Ambassador Ephraim Evron at a meeting in which Evron asked what the United States will do if Syria and its Arab allies press for sanctions when the Security Council considers the Golan question today.

Following the meeting, Evron said only that he was "not worried" about the U.S. position. However, Haig is understood to have told him that while the United States considers the annexation illegal and might support a resolution reemphasizing that point, it will not permit moves to go further and vote any kind of sanctions, political, economic or diplomatic.

The U.S. position represents an effort to ease the severe strains that have troubled American-Israeli relations since last month when the Reagan administration voted for a Security Council resolution condemning the annexation of the Golan Heights, which were captured by Israel from Syria in 1967. As a further gesture of displeasure, the United States also suspended a new strategic cooperation agreement with Israel and postponed decisions on foreign aid requests intended to help the Israeli defense industry.

Those actions brought an unprecedented burst of bitter public criticism from Israeli Prime Minister Menachem Begin. However, U.S. officials, instead of responding to Begin, have taken the position privately that he had been put on notice about Washington's attitude toward his conduct and that the situation should be allowed to cool off.

Although the State Department deliberately refused before yesterday to say what its position would be toward sanctions, it has been increasingly clear in recent days that the administration believes that its message has been understood by Begin and that it now is time to put the Golan issue aside and focus on other aspects of the Mideast peace process.

Most immediately, the administration wants to emphasize the need for a breakthrough in the long-stalled Egyptian-Israeli negotiations on limited self-government for the Palestinian occupants of other Israeli-occupied territories. In order to give momentum to the flagging peace process, the United States now is pointing toward an autonomy agreement before the end of April when Israel is scheduled to return the last part of the occupied Sinai Peninsula to Egypt.

Haig, who has been accused of not paying sufficient attention to the autonomy talks, reportedly is considering appointment of a special, high-level U.S. negotiator to try to speed up progress and, if the talks show signs of a potential breakthrough, involving himself personally through a shuttle-diplomacy mission between Cairo and Jerusalem.

If a special negotiator is named, U.S. officials expect it will be Brent L. Scowcroft, a retired Air Force general who served as national security adviser in the Ford administration.

However, Haig is described by the officials as still undecided about whether to recommend that President Reagan appoint a special negotiator and probably will not make up his mind until he discusses the situation later this week with Alfred L. Atherton Jr., U.S. ambassador to Egypt, and Samuel W. Lewis, the ambassador to Israel.

In addition, Haig, who will take part in a special meeting of North Atlantic Treaty Organization foreign ministers in Brussels Monday, plans to visit Jerusalem and Cairo immediately afterward to discuss the autonomy talks and other problems with Begin and Egyptian President Hosni Mubarak.

In another Mideast development yesterday, State Department spokesman Dean Fischer said that reported Israeli overflights of Iraqi territory "are unhelpful and likely to increase tensions in the area." Fischer did not specifically confirm that overflights were made by U.S.-provided F15 jets, but said American views have been made known to Israel.