Standing side by side in the White House Rose Garden, President Clinton and Israel's new prime minister, Ehud Barak, pledged yesterday to restore the lost momentum of Middle East peacemaking and with it the traditionally warm relations between Israel and the United States.

Before heading into a private 2 1/2-hour meeting, the two leaders vowed to capitalize on Barak's overwhelming electoral victory in May to revitalize peace negotiations between Israel and its neighbors that were largely frozen under Barak's predecessor, Binyamin Netanyahu.

"Mothers, fathers and children all across the Middle East yearn for the dawn of a new era," said Barak, who arrived here Wednesday night for his first visit as prime minister and will return to Israel next Tuesday. "We cannot let their hopes down."

A senior Israeli official told reporters after the meeting that he expected "a very serious attempt in the coming weeks to restart the negotiations with Syria" over the terms of a peace agreement centering on the Golan Heights, the strategic plateau that Israel captured in the 1967 Middle East War.

Barak told Clinton that Israel is ready for "painful compromise" over the Golan, the official said. He added, however, that the Israeli leader emphasized that "the depth of the Israeli withdrawal" will depend on Syria's commitment to peace, including its willingness to fight terrorism and share water resources.

Administration officials were able to provide few details of the meeting. But a senior administration official who spoke to the president afterward described it as "very, very positive" and noted that the discussions with Barak would continue at the presidential retreat at Camp David, Md.

Barak was scheduled to spend the night at Camp David, then return to Washington this morning for breakfast with Secretary of State Madeleine K. Albright, followed by a meeting with Secretary of Defense William S. Cohen. Barak then flies to New York for meetings over the weekend with major Jewish groups. He returns to Washington for a White House dinner Sunday night, followed by another meeting with Clinton on Monday.

Barak's warm reception contrasted sharply with the chilly one accorded last year to Netanyahu, who was pointedly not invited to meet with Clinton when he traveled here to meet with Jewish organizations. Administration officials largely blamed Netanyahu's hard-line policies for the sorry state of Arab-Israeli relations during his tenure, and they clearly have high hopes for his successor, a much-decorated former general and protege of the late Yitzhak Rabin.

Administration officials have been particularly encouraged by Barak's success at assembling a large governing majority and a dovish cabinet, as well as his conspicuous efforts to extend an olive branch to Palestinian leader Yasser Arafat, Syrian President Hafez Assad and other Arab leaders.

Clinton has made no secret of his eagerness to conclude a peace deal in the 18 months he has remaining in office, remarking on Tuesday night that he was as "eager as a kid with a new toy" to meet with the new prime minister.

The same mood of optimism pervaded today's Rose Garden appearance, where Clinton praised Barak as a worthy heir to Rabin and vowed that "as Israel again walks bravely down the path of peace, America will walk with you, ready to help in any way we can." Barak, for his part, said he came to Washington as an agent of "change and renewal" and reiterated his pledge "to inject new momentum into the peace process and to put it back on all tracks."

For all the good feeling, administration officials say they are under no illusions about the hurdles that lie ahead. One has already surfaced: In interviews over the last week, Barak has floated the idea of postponing full implementation of the Wye River accord, which calls for additional Israeli withdrawals from the West Bank and was reached after agonizing negotiations outside Washington last fall.

With U.S. backing, the Palestinians have insisted that Barak carry out the accord--frozen by Netanyahu--without delay. "I don't think there is any flexibility on that," Hassan Rahman, who represents the Palestinian Authority in Washington, said in an interview. "Wye is the litmus test for Mr. Barak."

At the White House yesterday, Barak said Israel is "committed to live up to" the Wye accord. He added, however, that Israel would prefer to delay carrying it out until the resumption of so-called final status talks with the Palestinians, which are aimed at settling such pivotal issues as borders and the future of Jerusalem.

But he said such a delay would occur only "through an agreement with Arafat after mutual, open, frank and direct discussion."

The senior administration official who spoke with Clinton after the meeting said Barak assured the president that Israel would be "scrupulous" in terms of living up to its obligations under previous agreements with the Palestinians, but also "vigilant" about protecting its own security.

On the sensitive issue of West Bank settlements, Barak reiterated previous statements that he was "not going to build new ones" but would not dismantle existing settlements. "Israeli citizens are living in them," he said. "They came to these places [with] approval of the Israeli government."

"I believe in strong blocks of settlements that will include most of the settlers in [the West Bank] and the Gaza Strip," Barak added, apparently excluding isolated hilltop settlements--sometimes consisting of little more than a trailer or two--that Palestinians deem particularly provocative.

CAPTION: (Photo ran on page A01) All Smiles

President Clinton gives new Israel Prime Minister Ehud Barak a warm welcome on his first visit to Washington as both leaders pledged renewed efforts toward restoring the lost momentum of the Middle East peace process.

CAPTION: Israel's new prime minister, Ehud Barak, is welcomed to Washington by President Clinton in the Rose Garden. Barak will also visit Camp David and New York.