No Israeli leader has faced a cooler reception than Prime Minister Yitzhak Shamir is likely to encounter on his visit here this week, the performance of his government having strengthened U.S. resolve for a new approach in the United Nations toward Israel -- after the Gulf crisis ends.

While President Bush's decision to open talks with Baghdad won worldwide applause, Israel's reaction stunned Washington. Foreign Minister David Levy's "warning" to Ambassador William A. Brown that the United States must dismantle Iraq's military power, even though the United Nations never voted any such mandate, did not change Bush's Gulf policy. But it reinforced U.S. inclination to move away from its traditional role as Israel's protector in the United Nations.

The successful experience at the United Nations in confronting Saddam Hussein may spell an end to the longtime U.S. practice of shying away from any U.N. move affecting Israel. Although Levy's "warning" had no impact on Gulf policy, it strongly underscored Bush's troubles in dealing with Israel and thus invigorated new U.S. plans to transform Washington policy.

The world has changed for the tough prime minister. Bush and Secretary of State James A. Baker III privately accuse Israel of breaking its word and scuttling Shamir's Palestine election plan early this year. With Bush refusing a single telephone chat with Shamir ever since, the implication from Israel last week that Bush may sell out his principles in the Gulf angered the president's men.

This hardens the conclusion drawn from the U.S. experience of working closely with the United Nations against Saddam. The administration wants to collaborate with the world organization -- after the Gulf crisis ends -- in dealing with Israeli-occupied territories.

"What the United Nations did for us {regarding Iraq} makes it damn difficult to ignore it on Arab-Israel problems," a State Department official told us. Another policy maker said privately it would be "foolish to squander" the political power built up by Bush's adroit use of the United Nations and its Security Council. Thus, the United States is prepared to not veto a pending U.N. resolution, bitterly opposed by Israel, to set up a Mideast peace conference -- unless the administration construes it as "linkage" satisfying Saddam's demand.

All this is anathema to Shamir, and Bush is well aware of it. But the president wants no irritants when Shamir walks into the Oval Office Tuesday. Bush will give no suggestion of exerting pressure on Israel. He will show no nastiness and will ignore his own sour memory of wasting a year pushing Shamir's election plan before the prime minister himself killed it.

The decision to be a polite, considerate host is firm, no matter what grievances Shamir digs up or how bitterly he complains that Bush's treatment of Israel in the Gulf crisis has ignored the Jewish state's claimed strategic importance to the United States.

Instead, Shamir will be reminded of the United Nations' stalwart backing for the military buildup in the Persian Gulf, the Arab contribution to the anti-Saddam coalition and the successive near-unanimous votes in the Security Council supporting the United States. The suggestion Bush will leave hanging in the air for Shamir to ponder: Since the United Nations has worked so well in the Gulf, it should be tried elsewhere -- as on the Palestinian question.

If he operates true to form, Shamir will see what is coming and lash out at the United Nations as a stacked deck against Israel's interests. In truth, it often seemed to be just that when the then-mighty Soviet Union corralled its Arab clients and the entire communist world to impose one punitive vote after another against Israel. Often a minority of one, the United States guarded Israel in the Security Council with a procession of vetoes.

But Moscow and Israel have become friends, with diplomatic exchanges in the offing. Israel is now in Moscow's debt for lifting emigration barriers and official Israel-bashing has been stopped cold in Moscow. Mikhail Gorbachev wants desperately to be at the table in settling the Arab-Israeli struggle.

As for Israel's other U.N. tormentors, the "communist world" no longer exists, and even Syria has become a Washington ally in the Gulf. After the Gulf crisis cools, the United States will push both Syria and Saudi Arabia to recognize Israel as a first step in forcing Israel to give Palestinians the right to govern themselves.

These are the new facts of life Shamir faces in Washington this week. He will be doing himself and his nation a favor if he lays aside bellicose complaints that the Americans are not tough enough against Iraq and instead comes to terms with the changed world.