If there is a collision in the offing, it may become apparent soon, because the Israeli prime minister and Bush will be meeting next week at the White House.

This week's surprise announcement of the meeting slated for Monday comes as the Bush administration faces growing international pressure to produce a timetable and a detailed set of proposals for getting Israelis and Palestinians back to the negotiating table and ending their conflict.

Ironically, ideas that Sharon himself initiated, and which were subsequently picked up by the Bush administration, have brought to the surface deep differences between Jerusalem and Washington on how to proceed in Israeli-Palestinian peacemaking.

On the face of it, Sharon seems to have been extremely adept at getting his positions across:

•Sharon convinced Bush that Palestinian Authority President Yasser Arafat is part of the problem, rather than part of the solution.

•Sharon's prodding finally led Bush to declare his "deep disappointment" in the Palestinian leader.

•Sharon persuaded the Bush administration that the Palestinian Authority must undertake comprehensive reforms if it is to become a trustworthy neighbor to which Israel can make concessions.

•Sharon came up with a grand scheme for a regional peace conference this summer, which has become the cornerstone of America's peace policy in the Middle East.

Yet now, it seems, all these ideas may boomerang on the Israeli prime minister, forcing him into political moves he would rather delay. The trouble for Sharon is that while American leaders accept his package in principle, they differ over the purpose, timetables and other key details.

For example, U.S. officials see Palestinian reform and an international peace conference as a recipe for kick-starting substantive peace talks between Israel and the Palestinians. Some officials now suspect that Sharon sees those elements as a means of buying time and putting off meaningful dialogue with the Palestinians.

By putting his ideas on the table, Sharon may have inadvertently set off a process leading inexorably to a showdown with Washington.

The perception gap between Jerusalem and Washington was apparent during recent visits to the region by William Burns, the U.S. assistant secretary of state for Near Eastern affairs, and CIA Director George Tenet.

In a meeting with Burns, Sharon argued that Arafat is incorrigible, and that as long as he is in power there is no chance of a cease-fire or of political progress.

Arafat must be sidelined — including him in the reform process would be "a cardinal error," Sharon said.

Burns countered that only Arafat could give grassroots legitimacy to the reform process, and that if Arafat carried out the necessary reforms he could still be a player.

Sharon's close advisers acknowledge that the prime minister's greatest fear is that Arafat will take charge of the reform process, pretend to go along with it, regain international support and whip up pressure on Israel to make concessions.

"The whole idea is to replace the Arafat system of terror, corruption and internal repression, and it's obvious to us that Arafat can't change the system he personifies," says Danny Ayalon, Sharon's foreign policy adviser and ambassador-designate to Washington.

Sharon and his advisers also seem to have more stringent demands for Palestinian reform than the United States.

On reform of the security services, Sharon says that unifying the services under a single command is meaningless unless the various militias — such as Tanzim, Hamas and Islamic Jihad — are disarmed.

On political reform, Sharon's advisers talk about separation of powers, not merely new elections.

But the biggest difference is over the relationship between reform and peacemaking. For Sharon, reform is a condition for bilateral peace talks with the Palestinians, while the United States says reform and peace talks should proceed simultaneously.

The legitimate demand for reform, U.S. officials say, must not be used to delay the peacemaking process.

Sharon and the United States also have very different notions of what the international Middle East peace conference should be about. According to Ayalon, Sharon views the conference as a kind of open-ended "peace club" in which members with peace credentials like Egypt, Saudi Arabia, Jordan and Israel discuss ways of promoting regional stability.

"We see the conference as a means of establishing a peace coalition of Middle Eastern moderates as a counterweight to the war coalition, which we see with Iran, Iraq and Syria," Ayalon says. "But it is not meant to be a substitute for bilateral negotiations with the Palestinians."