The Reagan administration yesterday rejected a statement signed Sunday by Palestine Liberation Organization leader Yasser Arafat, saying it did not recognize "in a clear and unequivocal way" Israel's right to exist and therefore does not meet U.S. conditions for dealing with the PLO.

In identical responses, the White House and State Department reaffirmed the policy, in effect since 1975, that the United States will neither recognize nor negotiate with the PLO until it accepts Israel's right to exist and U.N. Security Council resolutions 242 and 338, which have provided the framework for efforts to resolve the Arab-Israeli conflict.

"We have indicated this must be done in a clear and unequivocal way," said White House deputy press secretary Larry Speakes and State Department spokesman Dean Fischer. "The statement by Arafat does not meet our conditions."

Although they would not say so publicly, U.S. officials appeared to be in agreement with Israel's contention that the Arafat statement was not a significant departure in Mideast diplomacy, but a propaganda ploy aimed at winning world sympathy and support for the PLO, whose military forces are under Israeli siege in West Beirut and under pressure to leave Lebanon.

The U.S. statement implied that the administration regards the question of PLO recognition as a side issue that could divert attention from the efforts of President Reagan's special Mideast envoy, Philip C. Habib, to negotiate relocation of the PLO from Lebanon to other Arab countries.

Habib, meanwhile, yesterday received a strong vote of confidence from Reagan following revelations that the retired Foreign Service officer has been a paid consultant to the Bechtel Group Inc., an international engineering firm that has extensive business interests in the Arab world.

At Reagan's behest, the State Department issued a formal statement that called Habib "one of the outstanding public servants of this country" and said that he has "the full confidence and support" of Reagan and Secretary of State George P. Shultz, who is former president of Bechtel.

The dismissal of Arafat's move came a day after the PLO leader touched off diplomatic tremors by giving to Rep. Paul N. (Pete) McCloskey Jr. (R-Calif.) a signed, one-sentence statement saying he "accepts all United Nations resolutions relevant to the Palestine questions."

McCloskey said afterward the statement effectively recognized Israel's right to exist, a step of potentially historic significance in the 34-year effort to achieve a Mideast peace settlement with Palestinian participation.

However, others on both the PLO and Israeli sides said the Arafat statement was simply a reaffirmation of the PLO's longstanding position that it will accept the existence of Israel in return for creation of a Palestinian state.

The official U.S. conclusion, after almost 24 hours of intense study, was that no new ground had been broken.

"We do not see it as anything new," Speakes said. Fischer, adding that PLO recognition of Israel "should not be buried in rhetoric in a way that cannot be identified later," responded to reporters' questions about what would constitute a PLO acceptance of Israel satisfactory to the United States by saying:

"We will know it when we see it."

Although Speakes said the United States is not seeking further clarification from Arafat, both he and Fischer stressed, in response to separate questioning, that if the PLO meets U.S. conditions on recognition of Israel, the United States would welcome the move and be willing to talk with the organization that serves as an umbrella for a variety of Palestinian factions.

Fischer also told reporters that he "would tend to dismiss as idle speculation" the idea that the United States does not want the PLO to change its position toward Israel because of unrelenting Israeli opposition to what it regards as a terrorist organization or because Washington is seeking to break the PLO's power and influence in the Arab world. In private, U.S. officials said it was too early to assess what impact Arafat's statement might have on public opinion in this country or in areas like Western Europe.

However, a clear sign that Arafat's gesture has had some resonance in the Arab world came from Egyptian President Hosni Mubarak, America's closest ally among Arab leaders.

Egyptian sources indicated that a letter from Mubarak to be delivered to Reagan later this week by Egyptian Foreign Minister Kamal Hassan Ali will call for the United States to take a more flexible line toward the PLO.

Fischer said that Israeli Foreign Minister Yitzhak Shamir also is expected here shortly to confer with Shultz.

But he added that it is doubtful Shamir will be here at the same time as Hassan Ali.