The United States yesterday hailed the meeting between Israeli Prime Minister Shimon Peres and Morocco's King Hassan II as a "historic opportunity to further the cause of peace" in the Middle East. But U.S. officials privately said the talks were unlikely to produce any immediate Arab-Israeli breakthroughs.

The officials, who asked not to be identified, said the administration's enthusiastic public rhetoric praising Peres' unprecedented surprise visit to the king represented what one called "an expression of our best-case hopes for the meeting."

They added, though, that the preliminary U.S. assessment is to view the meeting in Rabat as important because of its potential long-range psychological effects. Specifically, the officials said, it could encourage other moderate Arab leaders to start thinking about breaking the Palestine Liberation Organization's veto power over direct talks with Israel.

PLO Chairman Yasser Arafat has used this power twice in the last three years to scuttle initiatives aimed at producing direct talks between Israel and Jordan's King Hussein. As a result, U.S. policy-makers have concluded that chances for progress in the peace process are virtually nil unless moderate states such as Morocco and Saudi Arabia are willing to brave the wrath of the PLO and the radical Arab governments and give Hussein the backing he needs to enter negotiations with Israel.

However, the officials stressed, such a change is at best a long-term hope, and they cautioned that there was no evidence to support speculation that Peres' trip to Rabat will become a springboard for a meeting with Hussein. Instead, they pointed to Arab world reaction -- harsh condemnation from radical states such as Syria and Libya, qualified endorsement from Egypt and cautious silence from Jordan and Saudi Arabia -- as a sign that the Rabat meeting has not caused any immediate changes in the positions of these countries.

In addition, the officials said, Hassan, despite his earlier important role in helping to arrange the historic 1977 visit of Egypt's Anwar Sadat to Jerusalem, has a more recent history of eccentric and unpredictable moves such as his spur-of-the-moment decision last year to form a union between Morocco and Libya.

As a result, the officials said, even though he is chairman of the Arab League, he must be regarded as an atypical figure who does not command wide influence among other Arab states and who, in his talks with Peres, has no mandate to do any more than repeat past Arab terms for peace with Israel.

Nevertheless, the administration went all out yesterday to endorse the Rabat meeting.

White House spokesman Larry Speakes said, "It symbolizes the change that has occurred in the Middle East and creates a context which can enhance the peace process."

"We applaud this courageous initiative by these two leaders, an initiative which the U.S. government strongly supports," the State Department said. "This is an historic opportunity to further the cause of peace in the region, and the U.S. government urges all governments to support these leaders."

U.S. officials emphasized, however, that any definitive judgments about the impact on Middle East events cannot be made until the United States has more information about what was discussed in Rabat.

The officials said they learned about the planning for the Rabat meeting last week just before the Moroccan government announced that Hassan was canceling a scheduled visit here this week because of "fatigue." However, the officials said that while the U.S. government went along with that cover, the United States did not play any intermediary role and was not invited to become a participant in the initiative.

They denied speculation that a visit to the Jordanian capital of Amman late last week by Thomas R. Pickering, U.S. ambassador to Israel, involved an attempt to draw Hussein into the Rabat talks. Pickering, they said, went to Amman in connection with Hussein's recently launched campaign for a larger Jordanian role in the affairs of the Israeli-occupied West Bank.

The officials also said that the Peres visit might spell an end to faltering plans for a Libya-Morocco union, an idea that had been opposed strongly by the United States because it feared close involvement by Morocco, a traditional U.S. ally, with a country that the United States regards as a major supporter of international terrorism.