President Reagan yesterday turned down Egyptian President Anwar Sadat's proposal for U.S. contacts with the Palestine Liberation Organization, but the disagreement did not seem to dampen the leaders' mutual satisfaction with two days of White House talks.

The Egyptian president, calling his PLO proposal "an option" and "an alternative" among several that exist, told a later afternoon news conference at Blair House that he will give Reagan time to study this and other ideas for advancing the Middle East peace process.

"It would not be fair" to ask Reagan for a quick decision without having time to discuss it with Israel, Sadat said.

Ninety minutes earlier, however, Secretary of State Alexander M. Haig Jr. told a news briefing that in the White House meetings Reagan had repeated the existing U.S. position on PLO contacts and had emphasized in this connection to Sadat that the United States must keep "all its commitments"

The U.S. refusal to recognize or negotiate with the PLO, unless that organization recognizes Israel, is rooted in a confidential pledge to Israel by then-secretary of state Henry A. Kissinger in September 1975.

Successive administrations have interpreted the pledge as a ban on all substantive diplomatic contacts with the PLO except in rare circumstances, and Haig gave no hint yesterday that this strict interpretation will be relaxed.

Despite the apparently unyielding U.S. position on the six-year-old commitment, Haig and Sadat pointedly left the way open for participation in Mideast peace talks by West Bank mayors and other Palestinian leaders who do not formally claim to represent the PLO.

This participation was called for the U.S.-sponsored peace accords between Egypt and Israel but has been rejected by the local Palestinians.

Saying goodbye to Sadat, the first in a series of Middle East leaders expected here in the next few months, Reagan declared that it was agreed that "the negotiations stemming from the Camp David peace process, will resume and succeed."

Reagan also pledged that the United States will continue to "play an important part" in the peace process.

On questions of Mideast peace, Reagan was in "essentially a listening mode" in the Sadat talks, awaiting the Sept. 9-10 visit of Israeli Prime Minister Menachem Begin and later visits from Jordanian and Saudi Arabian leaders, according to Haig.

The secretary of states said the White House talks involved the need to "get on" with the stalled negotiations on autonomy for Palestinians living in the West Bank and Gaza. But there was no indication from either the U.S. or Egyptian side that decisions have been made about when or in what way to go about it.

Reagan and Haig listed discussions of the "strategic threat" in the Middle East posed by Soviet military power and Soviet surrogates as a high-priority item in the White House talks.

Haig said there was "an almost total unanimity of views" with Sadat on this point and on the need to intensify U.S.-Egyptian colloboration to "vigorously resist Soviet direct or insppired aggression." In this connection, Haig reported that Sadat had written a letter to Reagan detailing his offer to permit the U.S. Rapid Deployment Force to utilize the strategic Egyptian military base at Ras Banas on the Red Sea. Haig noted tha the admnistration has asked Congress for money to facilitate U.S. use of the Egyptian installation.

While briefing reporters on today's talks, Haig made a slip of the tongue and spoke of Sadat's "poignant" discussion of Egypt's future with "President Nixon."

Reporters gasped and quickly corrected Haig, who served as deputy to Kissinger in the Nixon's White House chief of staff. Recognizing his mistake in substituting Nixon's name for Reagan's, Haig said it occurred "because I'm thinking ahead," which brought another gasp. He then explained he had been thinking "what I'm going to say next."

Sadat, who met Senate and House members on Capitol Hill after his final meeting with Reagan yesterday morning, said he was "fully satisfied" with all his discussions here.