Israeli Prime Minister Shimon Peres has known for weeks that the United States promised the Palestine Liberation Organization that it could participate in an international peace conference if it met certain conditions, informed Israeli government sources said today.

Although Peres' office was informed of the Jan. 25 promise made by Assistant Secretary of State Richard Murphy, these sources said, neither the Israeli Foreign Ministry nor Israel's ambassador to Washington, Meir Rosenne, was told of it -- an omission that led Foreign Minister Yitzhak Shamir to complain last night that he viewed the "change" in U.S. policy with "extreme gravity."

The alarm raised by Shamir and the calmer approach taken by aides to Peres underscored the polarization between the office of the Labor Party prime minister and the Foreign Ministry, which is dominated by the Likud faction of the "national unity" coalition government.

Such breakdowns in communications are commonplace between the offices of the prime minister and the foreign minister, sources said, and Israel's embassy in Washington reports directly to Shamir.

When Rosenne met Friday with Murphy and Michael Armacost, undersecretary of state for political affairs, he complained that Israel did not know about the Jan. 25 offer made to Jordan's King Hussein by the United States. In the offer, Washington said the PLO could participate in a peace conference if it accepted U.N. Security Council Resolutions 242 and 338 (which recognize Israel's right to exist within secure borders), expressed willingness to negotiate with Israel and renounced terrorism.

Hussein disclosed the offer in a speech Wednesday in which he said he had ended a year-long effort to work with the PLO leadership toward peace with Israel.

What Rosenne should have said, Israeli officials here said, is that neither he nor Shamir knew about the U.S. offer.

A Cabinet source said Trade Minister Ariel Sharon raised the question of the U.S. offer at the Cabinet meeting today and that Peres replied, "We don't know anything about any report which deviates from the agreements," referring to the 1975 U.S.-Israeli agreements barring talks with the PLO. The source confirmed that Peres' office was informed of the Jan. 25 U.S. offer to Hussein, adding: "The report he Hussein got did not show that the United States went one step forward."

Another senior Israeli official said that any change in U.S. policy -- if one exists -- is purely one of nuance. He added that "the Americans are sticking to the position that participation of the PLO in an international conference is conditional on Israel's agreement, and that will never happen." He was referring to a U.S.-Israeli understanding that no party will be able to participate in an international peace conference without agreement by all parties.