The United States is pressing Syria and Israel, pivotal players in the Middle East conflict, to accept a compromise and attend a proposed peace conference.

Administration officials believe Syrian President Hafez Assad must decide whether to adopt a moderate role in the Arab world or to continue his vehemently anti-Israeli policies.If Assad were to adopt a less hard-line position, Syria could accept Western - including U.S. - economic help. The officials who asked not to be identified said Assad could signal a change of heart by agreeing to a scaled-down role for the United Nations at the proposed peace conference to be attended by Israel and the Arabs.

In return, the officials say, the Israelis must also give ground on this issue.

Israel wants no U.N. role at the conference for fear it would turn out to be a tribunal and impose peace terms. Syria and other Arab nations are pushing for significant U.N. participation.

In addition, the Arabs want the conference to be a continuing event while the Israelis are seeking a single meeting followed by direct, face-to-face negotiations.

Secretary of James Baker concluded his fourth post-gulf war Middle East shuttle mission late last week but was unable to effect a compromise that would have put the parties at the peace table.

President Bush, though, still sees "real cause for optimism, and we will continue to work this process."

The United States, for the first time, has obtained firm assurances from Israel on what it would take for the Jewish state to attend a peace conference. Sources say the Israelis would accept a U.N. observer provided he did not have the right to propose suggestions or even to formally address the conference. Syria is unlikely to accept this formula.

For the time being, the action is in Syria. On Saturday, King Hussein of Jordan went to Damascus for talks with Assad on the prospects of peace in the Middle East.

Hussein was paying his second visit to the Syrian capital since the end of Persian Gulf war in late February. The king will brief Assad on his talks last week with Baker in Amman, Jordan.

Soviet Foreign Minister Alexander Bessmertnykh also saw Assad in Damascus recently as part of his separate Middle East peacemaking tour. Egyptian President Hosni Mubarak will see Assad next week.

The Bush administration believes one of its best Israeli cards is an acceptance by Saudi Arabia, Kuwait and the four other Persian Gulf states to sit down with Israel to discuss such regional issues as water supplies, the environment and disarmament.

"It implies a willingness on the part of Saudi Arabia to sit down and negotiate directly with Israel, something that no Arab country has ever been willing to do, save Egypt," a senior administration official said.