The United States, anticipating a redeployment of Israeli forces in Lebanon, has proposed that Israel consider fixing a "date certain" for total, unilateral withdrawal of its troops as a means of putting pressure on Syria to pull its forces out, informed sources said yesterday.

The U.S. plan, advocated by Secretary of State George P. Shultz and approved by President Reagan, was presented to Israeli officials in Jerusalem earlier this week by Reagan's special Middle East envoy, Philip C. Habib.

The sources said Shultz had become convinced that there is little chance of engaging Syria in a "friendly dialogue" and that a new approach is needed to achieve the withdrawal of all foreign forces from Lebanon.

Shultz and Habib were described by the sources as hopeful that if Israel publicly commits itself to leave Lebanon at a fixed time, Syria would appear as the recalcitrant party in the Lebanon crisis and would be subject to increased pressure from other Arab countries and the international community to be more cooperative.

However, the sources insisted that the move is not a repudiation of the agreement made between the United States and Israeli Prime Minister Menachem Begin's government following the Israeli-Lebanese peace accord worked out with Shultz's help seven weeks ago.

It was agreed then that Israel is not obligated to pull out of Lebanon unless there is simultaneous withdrawal by Syria and Palestine Liberation Organization forces in Lebanon under Syrian protection.

Instead, the sources stressed, the idea was presented to the Israelis as a "suggestion" or "trial balloon" for consideration as one option when the Begin government decides whether to stage a partial withdrawal that would remove its forces from central Lebanon and redeploy them in the south near Israel's northern border.

According to the sources, Habib was instructed to make especially clear to the Israelis that the United States is not changing its policy and will not pressure Israel to withdraw unilaterally from Lebanon against its will. The sources added that the Israelis accepted the idea in that spirit and, while unenthusiastic initially, agreed to consider the idea.

The first news of the latest U.S. approach was revealed by the Middle East Policy Survey, a Washington newsletter, in its issue scheduled for release today. The sources confirmed that the main outlines of the plan described by the newsletter are correct.

However, the sources disputed the newsletter's contention that it marks "a stunning change of policy," that the administration intends to "press" Israel to adopt a withdrawal date and that Shultz and Reagan conceived the plan "against the near-unanimous advice of their leading Middle East experts."

The sources said the president and Shultz took great pains to avoid Israeli suspicions and charges of bad faith by framing the proposal in a way that made clear it was a "suggestion for possible discussion" and not an American attempt to dictate Israel's future course in Lebanon.

Similarly, while the sources acknowledged that there is considerable skepticism among State Department officials about whether the plan has a chance of working, they denied the suggestion that Shultz had repudiated the advice of the department's bureau of Middle East affairs.

Instead, the sources said, the plan stems from Shultz's conclusion that the United States originally was too optimistic in believing that Syrian President Hafez Assad would cooperate in a Lebanon pullout, and that since the limited leverage available to Washington has not had any effect on Syria, the problem must be approached from a different angle.

During talks here two weeks ago, David Kimche, director general of the Israeli Foreign Ministry, made clear that Begin will soon respond to heavy domestic discontent over Israeli casualties by redeploying his forces in more defensible positions.

The United States fears that such a partial withdrawal will leave a void of authority in central Lebanon that could cause new outbreaks of civil war and make the Syrians even more recalcitrant.

The sources said the new U.S. proposal, originated by Habib, aims at getting Israel to couple its redeployment with announcement of plans for a "date-certain" withdrawal. The U.S. hope is that such a move by Israel would then make it increasingly difficult for Syria to justify its refusal to honor its promises to leave Lebanon once the Israelis do.

However, the sources acknowledged, many State Department officials believe Israel will reject the proposal as an overly naive idea that will convince Syria it can achieve its goal of dominating Lebanon by simply sitting tight until the Israelis have left.