Prime Minister Sharon’s visit with President Bush, set for this week, has the potential to be one of the most important of a leader of the Jewish state since the meeting of Presidents Weizmann and Truman, at which the American-Israel partnership was symbolically established. For if Messrs. Sharon and Bush can agree on the main features of disengagement, and especially on the line of the security fence and the borders it will establish, this will mark the first time since 1967 — or even 1948 — that Israel and America have actually agreed on the boundaries within which Israel has a right to stay put forever in any peace settlement with the Palestinian Arabs. And it will be the first time that they will have done more than agree to disagree about what these lines should be.

Given the importance of the moment, it is a remarkable thing that it has attracted so little attention. “Critics who still chastise the Bush administration for failure to ‘engage’ with the Israeli-Palestinian conflict seem not to have noticed that over the past several months the White House has been more deeply involved in trying to broker a breakthrough than at any time since President Bill Clinton’s Camp David summit in the summer of 2000,” writes the Washington Post’s Jackson Diehl, one of the few columnists to perk up to what he calls “these mostly secret and underreported parleys.” He is concerned that Mr. Bush might agree to something that is too favorable to Israel.

“By striking a deal with Sharon,” Mr. Diehl demurs, Mr. Bush “would put himself in the position of shielding the Israeli leader from international backlash while he proceeds to overturn the apple cart of the Middle East peace process and effectively confiscate 15% of the West Bank.” But the whole point of what Mr. Sharon is doing is that the “peace process”that the left loves so much has yielded nothing. Years of pursuit of a negotiated settlement has failed to disclose a single Palestinian Arab official — we’re not speaking of the occasional heroic dissident — who has been prepared to pursue anything but a deceitful demarche.

It is true that the plan Mr. Bush will be asked to endorse in a letter committing America for years to come is more generous than Mr. Clinton’s plan and gives the state of Israel a greater share of the land of Israel. But there are those of us who see this as precisely one of the virtues of what Prime Minister Sharon is seeking. No doubt there are those who reckon Mr. Clinton’s plan was not generous enough with the Arabs. The State Department is crawling with them.

But the logic of what is being proposed this week is clear. Only if Israel has an American guarantee can Israel allow itself to withdraw to this border unilaterally, without having to negotiate with a Palestinian leadership. So what Mr. Sharon is seeking would be a breakthrough. Far from dooming the peace process, it would establish an American commitment.

Such commitments aren’t always kept. In 1956, President Eisenhower promised David Ben-Gurion that America would enforce the freedom of navigation in the Straits of Tiran in exchange for Israel removing forces from Sharm el-Sheikh. In 1967 Egypt blocked the straits, effectively isolating Israel, and America did nothing. When Abba Eban mentioned the assurances to the Johnson White House, he was told that President Johnson could find no record of the original promise.

Still, Mr. Sharon has apparently decided that an American commitment is more reliable than one from the Palestinian Arabs. It’s an approach that has its risks. Yet that Mr. Sharon would consider it is a testament to the warmth, durability, and shared values of the relationship between Israel and America.