Senior Israeli government and military officials have concluded that the Israeli Army can and should be withdrawn from southern Lebanon by mid-May, at least three months earlier than originally planned, according to well-informed sources here.

The decision to accelerate the withdrawal reportedly was reached by Prime Minister Shimon Peres, Defense Minister Yitzhak Rabin and senior military officials within the past week. The shortened timetable that these officials now favor is still subject to approval by the Israeli Cabinet, but sources said major opposition is not anticipated there.

The sources said the second stage in Israel's three-stage withdrawal plan is now expected to be completed by mid-to-late April. The second stage, involving a pullback from positions the Israelis hold in the mountains of eastern Lebanon, is already under way and is benefitting from warmer than usual weather for this time of the year.

As part of the accelerated timetable, some areas of southern Lebanon that Israel planned to retain until the final stage of the withdrawal will be evacuated in the second stage, according to the sources. They said it then will be possible to complete the third and final stage, back to the international border, a short time later.

While the government's position on the Lebanon pullout is becoming clearer, reports of possible shifts on Israel's position toward the broader Middle East peace process prompted a denial by Uri Savir, Peres' chief spokesman.

"The reports of a change in Israel's position opposing prior negotiations between the U.S. and a joint Jordanian-Palestinian delegation are without foundation," Savir said. "Israel continues to support direct negotiations with a Jordanian-Palestinian delegation that does not include PLO members."

Peres has held a series of meetings over the past week with U.S. Ambassador Samuel W. Lewis to discuss various scenarios for talks but sources familar with these meetings say Peres has offered no concrete response to any of the ideas. His "attitude is positive" toward almost anything that would move toward Israel's goal of direct negotiations with the Arabs, according to one source.

Officials close to Peres say Israel is "ready to explore ideas on a first step" toward direct negotitions with the Arabs, and "if new ideas come up, we'll treat them seriously."

In Washington, a State Department official said the idea of a preliminary meeting in Washington without Israeli representation was "one of several suggestions that are possibilities" but stressed that the United States will require a lot more information before it can make a judgment about the idea, staff writer John Goshko reported.

What remain vague in the Israeli plans for withdrawal from Lebanon are the size and function of a "security belt" that Israel intends to establish north of the border, in Lebanon. Israeli officials insist the withdrawal from Lebanon will be total, but they also say they will conduct a "mobile defense" of northern Israel, suggesting frequent and regular Israeli Army patrolling of the security belt.

The security belt is supposed to be controlled by the South Lebanon Army, but that militia, trained and financed by Israel, has suffered widespread defections in recent weeks and is not considered capable of providing security in the territory on its own.

In the past several days, both Peres and Rabin have publicly suggested their growing support for an accelerated withdrawal in the face of continuing Israeli casualties from attacks by Lebanese Shiite Moslem guerrillas.

On March 12, speaking to soldiers at an Israeli Army base near the Lebanese port city of Tyre, Rabin acknowledged that the heavily Shiite areas east of Tyre -- now scheduled to be part of the final stage of the pullback -- might be evacuated in the second stage.

On Sunday, pressed for a withdrawal timetable on the CBS-TV program "Face the Nation," Peres said he expected the process to be completed in eight to 10 weeks.

Peres told a high school audience yesterday that the withdrawal "is being conducted as speedily as possible," adding that "today there is no political hindrance to withdrawing from Lebanon as soon as possible."

Peres also said he was confident that "a reasonable level of security can be provided for Israel's north through mobile defense, through the right kind of deployment of the IDF Israeli Defense Forces on our border."

The Israeli Cabinet adopted the three-stage withdrawal plan in January. Israel has never announced a definite timetable for the withdrawal, but senior officials said that the plan called for a pause of two or three months between each stage to assess the situation, and that they expected the process to be completed by late summer.

The shortened timetable that was described by sources here has not been formally adopted but was said to be an "understanding" reached at the top levels of the government and the military. Despite growing pressure to leave Lebanon as soon as possible, Israeli officials have been reluctant to acknowledge that they are accelerating the withdrawal for fear that this will be interpreted as a sign of weakness in the face of the Shiite guerrilla attacks.

As a result, the shortened timetable is likely to be portrayed here as a purely military decision, based on the Army's judgment of how best to protect northern Israel. Military planners have been permitted to decide how rapidly to complete each stage of the pullback, with the Cabinet's role confined to authorizing execution of each stage when the plans are presented.