Reagan administration officials, urging "extreme caution" in assessing a statement signed yesterday in Beirut by Yasser Arafat, said it did not seem to meet U.S. conditions for dealing with the Palestine Liberation Organization.

Early news accounts from Beirut suggested that the PLO chairman had clearly accepted Israel's right to exist and U.N. Security Council resolutions 242 and 338, the framework resolutions underlying Middle East peace efforts. The Reagan administration, like the Carter and Ford administrations, has endorsed former secretary of state Henry A. Kissinger's 1975 promise to Israel that the PLO must accept these points in order to qualify for a role in the peace process, including negotiations with or recognition by the United States.

Later reports from Beirut, however, indicated that the statement signed by Arafat was subject to various interpretations and did not explicitly mention any of the U.S. requirements.

In the view of a senior official monitoring the situation in the Middle East, yesterday's statement was short of the "clear and unequivocal" PLO acceptance that the State Department has repeatedly and recently said it is looking for.

President Reagan, returning to the White House from Camp David, fended off reporters' questions, indicating that he could not hear them over the roar of helicopters on the White House South Lawn.

Anson Franklin, assistant White House press secretary, said Reagan had been kept informed of the reports from Beirut. "We would recommend extreme caution in assessing the meaning of this development until we have a better understanding of it," said Franklin, in a statement also being made by State Department spokesmen.

There was no sign, despite widespread rumors to the contrary in recent days, that the administration is seriously contemplating a relaxation of its requirements for PLO recognition.

Khalid Hassan, a senior member of the Palestine National Council, the legislative body of the PLO, left Washington over the weekend after being unable to meet directly with any administration officials. Nonetheless, Hassan sent several messages to high officials through intermediaries, including well-known Palestinians who reside in the United States.

Hassan, describing himself as an unofficial part of the Arab League's recent diplomatic mission to the administration, urged in his contacts here that the United States take a firm stand for Palestinian self-determination. He also asked the United States to encourage and work with the Arafat leadership, which Hassan said is the most moderate and pro-American leadership possible under existing circumstances.

One senior State Department official on the receiving end confirmed that many messages from the PLO have been received indirectly in recent days. "What they have in common is that all of them are different, and none of them is sufficient to meet the U.S. conditions ," the official said.

In the view of State Department sources, the main Mideast diplomatic action at the moment is not between the PLO and the United States, a longstanding minuet that is seen as "a sideshow."

The central question, in the official view, continues to be the detailed arrangements for evacuation of surrounded PLO fighters from West Beirut. This is the main topic under discussion by U.S. special envoy Philip C. Habib in a round of talks with Middle East leaders.

The indications are that a number of Arab countries, Algeria, Egypt, Iraq, Jordan and Syria, are likely to accept some of the PLO fighters and perhaps members of their close families in an evacuation from Lebanon, if such an operation obtains the blessing of the Arab League.

A meeting in a day or two of a six-member special Arab League committee, including the PLO and several key countries, is expected to be an important part of this process. If the meeting is successful in moving toward Arab acceptance of a concrete evacuation plan, a foreign minister's meeting of the entire Arab League may be summoned to endorse the arrangement.

It now appears unlikely, according to the sources, that the PLO evacuation would be a two-stage operation as suggested to Reagan last Tuesday by the two official Arab League emissaries, Saudi Arabian Foreign Minister Saud Faisal and Syrian Foreign Minister Abdal Halim Khaddam.

Their "new ideas," as administration officials referred to them, called for removal of the PLO fighters from West Beirut to northern Lebanon as an interim step before their dispersal to other countries.

The proposals currently under discussion by Habib and the Middle East leaders, according to the sources, continue to call for the deployment of U.S. and French forces, perhaps joined by others, to monitor the withdrawal of the PLO fighters from West Beirut.