SECRETARY OF State Condoleezza Rice has rightly scheduled a return to the Middle East this week in an effort to prevent the collapse of an Israeli-Palestinian cease-fire. At stake is more than the tenuous truce that prevailed from February until last week and that gave Israelis and Palestinians the most sustained respite from terrorism and bloodshed in five years. The resumption of violence also threatens to disrupt the most important step toward peace in the region in years: Israel's planned withdrawal of its settlers and troops from all of the Gaza Strip and a small part of the West Bank beginning next month. Even if the evacuation goes forward -- and Israeli Prime Minister Ariel Sharon still insists that it will -- a pullout under fire could leave Gaza in chaos and wreck any chance for a resumption of the broader Israeli-Palestinian peace process.

The catalyst for the breakdown was provided last week by the Palestinian Islamic Jihad, a group headquartered in Damascus and sponsored by Iran that dispatched a suicide bomber to an Israeli shopping mall. Two days later the militant Islamic Hamas movement, which also stands to lose from a peaceful, well-coordinated Gaza withdrawal, began firing scores of rockets and mortar shells at Israeli homes. Israel responded by resuming arrests and assassinations of Hamas members, and by massing troops on Gaza's borders.

Mr. Sharon can hardly be faulted for responding to the Palestinian attacks, which killed a half-dozen Israeli civilians. But the Israeli military response risks playing into the hands of the Palestinian extremists. Palestinian President Mahmoud Abbas, whose own security forces fought gun battles with Hamas on Friday in an attempt to stop the attacks, could be critically undermined by continued Israeli intervention. Mr. Abbas's efforts to rein in the militants have been too weak; his continuing efforts to obtain the agreement of Hamas and Islamic Jihad to respect a cease-fire begin to look far-fetched. But if the moderate Palestinian president is shoved to the sidelines by Israeli military intervention, the result could be a post-withdrawal Gaza effectively ruled by Hamas and its allies.

Such an outcome might suit Israeli hard-liners determined to stop further territorial concessions or peace talks, but it would be a disaster for the Bush administration and U.S. interests across the Middle East. While Ms. Rice may not be able to save the cease-fire, along with the possibility of an Israeli-Palestinian accord over the withdrawal, she is right to try. That means demanding that Mr. Abbas, with support from Egypt, act decisively to impose his principle of "one authority, one gun" in the Palestinian territories, as well as holding Iran and Syria accountable for their meddling. It also means urging Israel to show restraint unless and until it becomes clear that Mr. Abbas cannot succeed. That would be a fateful and costly judgment -- and it is too soon to make it.