Israeli officials appeared today to have already rejected the reported U.S. proposal that Israel set a deadline for a unilateral total withdrawal of its forces from southern Lebanon.

A spokesman for Prime Minister Menachem Begin confirmed that U.S. envoy Philip C. Habib had discussed such an idea in his talks Monday with the Israeli leader and the spokesman said Israel rejected any unilateral withdrawal.

But it was not clear from his brief remarks to reporters whether Israel was against the idea of setting a deadline as an enticement to Syria to withdraw its troops or whether the spokesman was simply reiterating Israel's frequently stated opposition to the idea of a unilateral withdrawal from Lebanon.

The spokesman, Uri Porat, said that it was one of many ideas now before the Israeli government and that everything would be discussed, presumably at Sunday's weekly Cabinet meeting.

Furthermore, a senior Israeli official briefing foreign correspondents said that nothing Habib has suggested indicated any change in the basic U.S. position aimed at obtaining a simultaneous withdrawal of all foreign forces from Lebanon.

Habib met again today with Begin but no details of their discussions were made known by either side.

Israeli radio and virtually all the country's newspapers today gave extensive coverage to the report of the new U.S. proposal. They also quoted Foreign and Defense Ministry sources as saying it was "a nonstarter," "absurd" and "an admission of failure" by the United States in its efforts to arrange for a complete withdrawal of all foreign forces from Lebanon.

But again it was unclear just what was being rejected by the Israeli government and whether Habib had really proposed, as they seemed to imply, that Israel withdraw even if Syria refused to reciprocate.

Israel has always rejected the idea of pulling its forces out of Lebanon unless Syria and the Palestine Liberation Organization also withdraw their troops at the same time. Israel contends that if it withdraws alone, Syria and the PLO would simply fill the vacuum and once again become a threat to its northern borders.

It is not known whether any decision will be made before Begin meets President Reagan in Washington late this month.

Begin has sought to assure the Israeli public that the government will protect Israel's own security without bowing to any U.S. pressure on the withdrawal issue.

As Israeli casualties mount from attacks in Lebanon, Begin has been under growing pressure here to begin pulling the troops out.

But he has also tried to reassure both the Reagan administration and the Lebanese government that Israel will act only after close consultations with both of them and will try to devise a plan agreeable to all three.

This may not be easy. Lebanese Prime Minister Shafiq Wazzan said yesterday that Lebanon was opposed to a partial Israeli withdrawal unless it was part of a total pullout.

"We are not ready to accept what is called partial withdrawal and have explained all this to Habib," he said in Beirut after talks with Habib.

Syria's total rejection of the Israeli-Lebanese withdrawal accord signed seven weeks ago has put Israel as well as Lebanon and the United States in a delicate position.