The Reagan administration yesterday endorsed a four-point plan to defuse the Israeli-Palestinian confrontation in Beirut, as official sources reported the first substantial movement toward a negotiated settlement.

The U.S. stand, announced by State Department spokesman Dean Fischer, would bring "an end to the armed Palestinian presence in and around Beirut," thus going a long way toward accomplishment of the Israeli aim of neutralizing the Palestine Liberation Organization.

The U.S. statement did not spell out how this armed presence would be ended, but officials said the United States is seeking the disarming of the 5,000 to 6,000 Palestinian guerrillas trapped in Beirut and the relocation of at least their leadership to another country.

This is reported to be the central point of the negotiations between the PLO and the Lebanese government in Beirut, with special U.S. envoy Philip C. Habib standing in the wings to supply U.S. backing and international coordination.

Washington sources said that for the first time the Palestinian and Lebanese leaders have gotten down to business and are making progress. There has been more movement in the past 48 hours than at any previous time, an official said. But he cautioned that problems remain, and it is too early to breathe a sigh of relief. The State Department, with the departing Alexander M. Haig Jr. still at the helm, continued to coordinate the U.S. position in the Lebanon negotiations and to be the principal Washington channel for Habib.

At the same time, Haig's designated successor, George P. Shultz, received his first staff briefing on the Middle East situation, but so far has given little or no indication of his views.

"He asked all the right questions," said an official familiar with the lengthy briefing on the Middle East for Shultz at the White House yesterday. But White House officials, seeking to emphasize the continuity of policy, said Haig continues to be in full command of the chief U.S. diplomatic office.

"He's the secretary of state--fully, totally, legally, formally, without reservation, mentally or otherwise--and will be the secretary of state until such time as he leaves," said White House deputy press secretary Larry Speakes.

Haig, as matters stand now, may leave his office about Thursday, according to an informed official. Shultz is expected to return to California about the same time to wind up his personal affairs before returning for his Senate confirmation hearings and, after that hurdle, his new job.

If Haig does leave later this week, Deputy Secretary of State Walter J. Stoessel Jr. is slated to take over as acting secretary until Shultz is confimed by the Senate.

Haig's timetable depends to some degree on the Lebanese situation, especially the tense and potentially explosive confrontation around Beirut.

Both the Lebanese-PLO negotiations and the related decisions in Israel about further military action against the Lebanese capital are subject to change on almost an hour-by-hour basis, an official said.

Washington continues to exert heavy pressure on Israel to maintain the cease-fire that was announced Friday, following an urgent appeal from President Reagan and Haig. At the same time, the administration has been put on notice by the Israelis that they will move against the Palestinian forces in Beirut unless there is very early progress toward a negotiated solution.

The U.S. stand announced yesterday on the solution to the problem of Beirut was cast as an endorsement of positions taken by the Lebanese government at the United Nations and the Arab League foreign ministers meeting at Tunis, Tunisia. As spelled out at the State Department, the U.S. goals are:

* The deployment of the Lebanese army in and around Beirut.

* An end to the armed Palestinian presence in and around Beirut.

* The withdrawal of Israeli forces from the area around Beirut.

* The redeployment of all foreign forces in the Beirut area.

While similar to the Israeli goals, these U.S. objectives differ in some detail. However, Israel is likely to accept them as meeting the main points of its demand, according to diplomatic sources.

The Israeli Cabinet demanded Sunday that each of 15 component organizations of the PLO hand over its weapons to the Lebanese army and "without any exceptions" leave the country. The U.S. position falls short of this in that perhaps only the PLO leadership would leave. It is still unclear, according to officials, where the new home for the PLO leaders would be.

There was no mention in the Israeli Cabinet position of a pullback of Israeli forces from the area around Beirut, and yesterday's statement was the first time that such a disengagement had been publicly and officially endorsed by the United States.

Nonetheless, such a withdrawal has been under discussion privately by Habib and other officials for at least a week and is considered a logical Israeli concession in return for disarming of the PLO. This withdrawal would probably have to take place simultaneously with the PLO actions, according to sources.

The fourth U.S. point, redeployment of "all foreign forces" in the Beirut area, is intended to apply to Syrian military forces and the Syrian-officered Palestine Liberation Army, which is not part of the PLO, officials said.

An agreement and disengagement of forces in Beirut would not bring about the full Israeli withdrawal from Lebanon or solve the vexing political, economic and military problems of that country. But in the U.S. view, it would be a vital first step toward a broader solution.

According to the White House press briefing, Reagan has directed Habib to push for "a lasting cease-fire" and strengthening of the Lebanese government as well as withdrawal from the country of all foreign forces. Furthermore, "it is important that Israel be secure from terrorist attacks and that real progress is made on the Palestinian autonomy talks through the Camp David peace process," said spokesman Speakes.

Haig remained out of sight yesterday, except for a farewell reception for his senior staff, while his designated successor, Shultz, remained discreetly in the background, boning up on the Mideast but taking no direct hand in policy. The briefing at the White House on Mideast issues was conducted by Nicholas A. Veliotes, assistant secretary of state for Mideast affairs, and Mideast specialists of the National Security Council.

An NSC meeting orginally announced for yesterday was not held. The White House said the announcement had been an error.

Shultz also spent time with White House personnel officials yesterday discussing possible recruits to his State Department team. One official said Shultz was considering people for posts from deputy secretary on down, though no decisions have been made on how extensive the personnel change will be.

State Department officials said Shultz had been assigned a small personal staff and a temporary office on the department's seventh-floor "executive row" and was digging into a number of briefing books being prepared to acquaint him with major policy issues.