The Reagan administration, looking beyond the scheduled April 25 return of the Sinai Peninsula from Israeli control to Egyptian, plans a major new drive in May or June to try for a breakthrough in the negotiations over self-rule for the Palestinian inhabitants of Israeli-occupied territories.

The U.S. plan could be thrown into disarray if the Israeli government seizes on the strife in the occupied West Bank and Gaza Strip or the apparently Palestinian-inspired murder of an Israeli diplomat in Paris as pretexts to launch a new military strike against Palestine Liberation Organization forces in southern Lebanon.

But if the cease-fire along the Israeli-Lebanese border can be maintained, U.S. officials believe that Israel's withdrawal from the last occupied portion of the Sinai will go through on schedule and that, after a brief cooling-off period, the time will be ripe to put new priority emphasis on seeking an autonomy agreement.

The plan stems from soundings made by Secretary of State Alexander M. Haig Jr. during visits to Cairo and Jerusalem in January and February. While Israeli Prime Minister Menachem Begin and Egyptian President Hosni Mubarak then were reluctant to tackle the autonomy question seriously, they both assured Haig of their willingness to reassess the situation after the sensitive issue of the Sinai had been resolved.

For that reason, senior U.S. policy makers are understood to believe that a new try at breaking the deadlock over autonomy cannot be put off beyond this summer if the 1978 Camp David process is to be preserved as the principal framework for seeking a resolution of the Arab-Israeli conflict. The Camp David accords, which led to successful conclusion of an Egyptian-Israeli peace treaty, since have bogged down in failure to achieve the next goal--agreement between the two countries on an interim five-year period of limited self-rule for the 1.2 million Palestinians in the West Bank and Gaza.

The precise nature of the new U.S. approach still is being worked out, and administration officials say it is not certain yet whether the effort, in its initial stages, will be left to Haig's special autonomy representative, Richard Fairbanks, or whether Haig will make another attempt to inject himself directly into the talks as a mediator between Israel and Egypt.

Another problem involves the question of a location for intensified talks. Israel has been insisting that they be held at least partly in Jerusalem, but that is unacceptable to Egypt, which does not recognize Jerusalem as the capital of the Jewish state. As a compromise, the United States has suggested moving the negotiations to Washington, and U.S. officials are optimistic that the impasse over location can be worked out.

Looking beyond the immediate procedural problems, U.S. officials also concede that there is no way of gauging the chances for achieving a successful autonomy agreement. Although the talks officially resumed last fall after a long delay, there is still an enormous gulf between Israel's attempts to limit autonomy in ways that eventually will allow it to annex the territories and the Egyptian tendency to view an accord as paving the way for an independent Palestinian state.

In the U.S. view, there can be no agreement unless both sides are prepared to make significant concessions. In hopes of preparing the way for compromise, Haig used his recent Mideast missions to remind both governments that the autonomy agreement is supposed to be interim in nature and should not be used to try to determine the final status of the disputed territories.

Haig is known to have given both sides various U.S. "suggestions" about possible areas of compromise, and these subsequently were elaborated on by Fairbanks. Until now, however, not much has been done to follow up on the suggestions, and the U.S. view is that a return to intensive, high-level negotiations at an early date is imperative to make clear whether the elusive goal of an autonomy accord is achievable.