President Reagan yesterday ordered veteran diplomat Philip C. Habib to the Middle East amid a flurry of diplomatic efforts intended to head off a new outbreak of military action between Israel and Syria.

The White House announced that Habib, who held high posts in several recent administrations and retired three years ago as undersecretary of state, will visit Lebanon, Syria and Israel aand Reagan's personal envoy on the continuing crisis.

The Habib mission and other U.S. efforts were described by State Department sources as an effort to buy time, in hopes of making it politically feasible and attractive for Syria to withdraw its antiaircraft missiles voluntarily from Lebanon's Bekaa Valley.

In Jerusalem, Prime Minister Menachem Begin indicated that Israel would delay military intervention in central Lebanon during the Habib visit, but he stressed the U.S. efforts to resolve the crisis have yielded no results.

Syrian Foreign Minister Abdul Halim Khaddam, in Beirut for talks on Lebanon's internal crisis, welcomed the U.S. mission, but warned that "nothing will be accomplished" unless Israel alters its demands for withdrawing the missiles.

Israel has made clear that the presence of the Syrian antiaircraft weapons is unacceptable, charging that it violates an understanding between the two countries during the 1975-76 Lebanese civil war.

Israeli leaders have left little doubt that they are prepared to order military action, presumably air strikes against the Syrian batteries, if they are not removed swiftly.

Israeli Ambassador Ephraim Evron personally delivered to Reagan a message from Begin yesterday reportedly saying that Israel will grant additional time for a potential diplomatic solution through the efforts of Habib and others.

But Begin also is reported to have made it clear that Israel insists on removal of the Syrian weapons, and that time to do so is not unlimited.

Habib, 61, may leave Washington early as today, according to diplomatic sources, heading first to Lebanon and Syria before going to Israel about Sunday with results of his talks in the other capitals.

He is being given a U.S. Air Force plane in the Middle East, making it possible for his to shuttle between various capitals, if this seems warranted, with a minimum of difficulty.

Reagan also received a message, described by Saudi radio as "an important telegram" relating to the situation in Lebanon, from the Saudi Arabian head of state, King Khalid.

Meanwhile, Soviet Ambassador Anatoliy F. Dobrynin came to the State Department at his request for an unannounced meeting with Undersecretary of State Walter J. Stoessel Jr., apparently to deliver Moscow's views about the latest turn in the Lebanese situation.

There is little doubt that the Israeli Air Force has the ability to knock out the Syrian surface-to-air missiles, though at a cost in men and material. What happens next, if the Israelis do move against the weapons, is the source of the most serious concern in several capitals.

Syrian President Hafez Assad would suffer a grievous, almost humiliating blow if his antiaircraft missiles were destroyed and he were unable to mount a strong and credible response.

Failure to respond could endanger his leadership at home, and a powerful response could bring new death and destruction and court an even more serious round of escalation.

State Department officials indicated that Assad has agreed to meet Habib as part of the American's diplomatic effort. The Syrian president was reported to have been miffed early last month that Secretary of State Alexander M. Haig Jr. skipped the customary visit to Damascus as part of his whirlwind Middle East tour.

For that reason, Assad refused to accept a visit by Deputy Assistant Secretary of State Morris Draper in Haig's stead. Draper, a specialist in the are, will accompany Habib to the Middle East.

There is no clear signal, according to State Department sources, that Syria is ready to remove the antiaircraft missiles, which were placed in eastern Lebanon after a series of military moves and countermoves over several weeks involving Lebanese Christian forces, Syrian and Israelis.

The most tangible prospect appears to be discussions in Beirut by Khaddam, the Syrian foreign minister. Resolving the complex conflicts on the ground in Lebanon between the contending local forces could give Syria a reason to remove its weaponry, in the U.S. view.

Resolving such conflicts in Lebanon has proven to be agonizing and protracted at earlier turning points in that country's bloody past.