The United States has persuaded Israel to delay for a few days its troop withdrawal from the Chouf mountains of Lebanon, but administration officials said yesterday that no decisions have been made about moving units of the multinational force into that wartorn area after the Israelis leave.

The officials said Israel, which had planned to begin redeployment by the weekend, agreed to a brief delay while arrangements are made for the Lebanese army to move into the Chouf where Christian and Druze Moslem militias are engaged in renewed fighting.

However, U.S. officials and other diplomatic sources stressed that President Reagan's special Mideast envoy, Robert C. McFarlane, is not working on a plan to provide the Lebanese forces with backing from the multinational peace-keeping force of U.S., French, Italian and British troops.

There has been persistent speculation that the force, whose activities are confined to Beirut and its environs, will be redeployed at the request of Lebanese President Amin Gemayel as a "confidence-building" backup for Lebanese forces sent into the Chouf.

That speculation broke out anew yesterday on McFarlane's arrival in Rome to consult Italian Prime Minister Bettino Craxi and Foreign Minister Giulio Andreotti.

But U.S. officials, conceding that consideration of an expanded role for the force might become necessary, stressed that the United States and its allies first want to see whether the Christians and Druze can agree on allowing Gemayel's forces control of the Chouf.

The officials said McFarlane was not carrying a specific U.S. plan but was engaged in exploring allied views about possible future roles for the multinational force. After his talks in Rome, they said, he is to visit Paris and London for similar discussions.

White House spokesman Larry Speakes, briefing reporters in Los Angeles, said: "It is still premature to define what an expanded role of the MNF might be when the Lebanese armed forces are deployed in the area . . . .

"There have been discussions with various people about contingencies, and it certainly is a logical topic for us to be reviewing. However, in the absence of some detail concerning the political situation which will prevail in the area, it is premature to make decisions or even to make firm recommendations."

Earlier contingency plans drawn up by force members to handle a possible expanded role call for the French to provide the principal multinational force in the Chouf, with Italians and some U.S. Marines helping the Lebanese patrol the highway between Beirut and Damascus.

Under that plan, most of the Americans would remain in the Beirut airport area.

The United States has about 1,200 Marines in the Beirut area and another 800 on nearby ships. Until now, the administration has been very wary of agreeing to Gemayel's repeated requests to expand the multinational force's size and role because it fears that Congress might balk.

France has about 2,000 troops in the force, and the Italian contingent numbers 1,400. Britain has made a token contribution of 100 men, and the administration has been trying to induce other friendly countries to follow suit.

U.S. sources said Israel, which plans to redeploy its forces in southern Lebanon along the Awwali River, had intended to begin its pullout from the Chouf by the end of the weekend and complete it by the Jewish new year, Sept. 7-8.

However, the sources continued, the Israelis agreed to a nonspecific delay of "a few days" after McFarlane made such a request of Defense Minister Moshe Arens late Tuesday.

MacFarlane told Arens that there are "positive signs" that an agreement might be worked out between the Christians and Druze on putting Lebanese forces in the Chouf if more time is available for negotiation.

On Wednesday, Arens persuaded Prime Minister Menachem Begin and Foreign Minister Yitzhak Shamir that Israel should accede to the request as a gesture to maintain improved relations with Washington. Arens and the army chief of staff, Lt. Gen. Moshe Levy, then went to Lebanon where they met with Israeli commanders near Damour to explain the delay.

The sources said the Israelis have refused to specify how long they will wait and have relied instead on the "few days" formula in discussing the delay with U.S. officials.

However, the sources added, the general supposition is that Sept. 7-8 is still Israel's target for redeploy- ment and that the Begin govern- ment will not let itself fall significantly behind that timetable.