To advance a two-state solution to the Israeli-Palestinian conflict, President Bush needs the support and involvement of Saudi Arabia.

The Saudis last week cautiously expressed interest in attending a regional peace conference Mr. Bush had proposed for the fall, provided the meeting tackles the core issues dividing Israel and the Palestinians.

The Saudis haven't done Mr. Bush any favors. A dialogue that would bring them to the table would have to include the status of Jerusalem and the future of Palestinian refugees, and the Israelis are resisting a discussion of either at this time.

Mr. Bush's commitment to reviving the peace process is on the line now.

He and Secretary of State Condoleezza Rice, who was traveling in the region last week, can try to persuade Israel to engage on these fundamental questions, or they can initiate pre-conference sessions to hammer out compromises on other issues that would serve as a prelude to a substantive meeting in the fall.

That's a tall order for a president who has neither demonstrated the diplomatic acumen nor invested the political capital to restart peace talks. Israel is hesitant to take on these tough issues while Palestinian Authority President Mahmoud Abbas is reasserting his authority after a spring of internecine Palestinian warfare.

Fighting between the nationalist, secular Palestinian movement headed by Mr. Abbas and the Islamic militant group Hamas led to the dissolution of the elected Hamas-led government in June, and to a geographic split. Mr. Abbas has re-formed the Palestinian Authority in the West Bank, which has won the backing of the international community though it remains a work in progress, and called for new elections. Meanwhile, the Hamas leadership and a million Palestinians remain isolated and confined to the Gaza Strip.

Mr. Bush would have to move forcefully and decisively to change the present stalemate, a formidable task with only 18 months left in office. In the absence of rigorous, tough diplomacy, which has been sorely lacking on this most intractable front, a peace conference would seem little more than a superficial gesture.

Then again, Mr. Bush and his chief diplomat could surprise everyone by initiating and overseeing back-channel negotiations as Israeli Prime Minister Ehud Olmert and Mr. Abbas work out accommodations on immediate concerns, such as checkpoints and Palestinian prisoners, which they discussed when they met in Jericho on Monday.

If Mr. Bush wants to be remembered for something other than the dissolution of Iraq, an independent Palestinian state and a secure Israel would be a worthy challenge for a lame-duck president. He has nothing to lose.