he last thing Israel should be doing at this moment of hopeful fluidity in the Middle East is slowing down a new American-backed peace plan. Yet that is what Prime Minister Ariel Sharon seems to have in mind by letting it be known that he will not be ready to move ahead on the newly published "road map" of mutual concessions when Secretary of State Colin Powell calls on him this weekend.

Instead, Mr. Sharon wants to wait nearly another month, until he meets with President Bush in the White House, and then press for changes in the proposal, whose sponsors also include the European Union, Russia and the United Nations.

Nobody expected Mr. Powell's mission to be easy. But to be told in advance that he is wasting his time does neither side any good. Mr. Powell can address Israeli concerns. This is not the first time Mr. Sharon has tried to undercut Mr. Powell's authority. He is only making it harder for Washington to win wholehearted Arab commitments to the peace plan's crucial first steps. On this trip, Mr. Powell will also meet with the new Palestinian prime minister, Mahmoud Abbas, and the leaders of Jordan, Egypt and Saudi Arabia.

Mr. Sharon's plans lend credence to Palestinian charges that Israel wants to stall movement on the road map until the 2004 United States presidential campaign, hoping that domestic American political considerations will then preclude further pressure from Washington to take difficult steps for peace.

The road map proposal takes a three-stage approach to Palestinian statehood and a permanent peace agreement. It begins with steps to re-establish some confidence between the two sides, by, for example, requiring the Palestinian Authority to move effectively against terror and directing Israel to ease restrictions on Palestinian movements and dismantle settlement outposts set up in the past two years.

Only then does it move on to historically irreversible steps, like recognizing Palestinian statehood and insisting on the final resolution of all outstanding claims, including the Palestinian refugee issue. The essence of the plan is its carefully designed sequencing arrangement. Mr. Sharon wants to unravel this sequencing by insisting that the Palestinians renounce all refugee claims before Israel even agrees to accept provisional Palestinian statehood.

Although the plan is not supposed to be open to far-reaching amendments, Israelis and Palestinians should be encouraged to discuss their concerns freely. Mr. Sharon should not pass up the opportunity to do so with America's secretary of state.