Israel’s prime minister, Benjamin Netanyahu, and the Palestinian president, Mahmoud Abbas, will open talks on a two-state solution on Thursday in Washington. These will be the first direct negotiations between the two sides in 20 months, and there will be an early test of the two leaders’ seriousness of purpose.

Mr. Netanyahu’s moratorium on settlement construction expires on Sept. 26. Mr. Abbas has threatened to withdraw from the face-to-face talks if the moratorium is not extended; Mr. Netanyahu has signaled that he plans to let building resume. The two leaders may be jockeying for political advantage, but the idea that the negotiations could collapse before they really have a chance to get off the ground is worrisome. The Obama administration needs to work hard — and creatively — to help find a solution to get by the Sept. 26 flash point.

Palestinians are justifiably concerned that settlement projects nibble away at the land available for their future state. If Mr. Abbas is engaging in serious direct talks, Mr. Netanyahu should have no excuse to resume building. To Mr. Netanyahu’s credit, settlement has slowed considerably since the 10-month moratorium was put in place, and that has improved the atmosphere for negotiations.

There are other positive currents. Violence against Israelis is down. Palestinian security forces are increasingly competent at policing the West Bank. Palestinian authorities have clamped down on incitement, including removing imams and teachers who encourage attacks against Israelis. More can still be done.

The biggest plus may be President Obama’s commitment. His predecessor ignored the conflict for seven years before arranging a peace conference in 2007 that had insufficient preparation and inadequate presidential investment. Mr. Obama made Middle East peace an early priority. He correctly sees the Israeli-Palestinian conflict as a factor in wider regional instability. He is more balanced in his approach that his predecessor, and his chief envoy, George Mitchell, has spent countless hours bringing the parties together.

There are serious obstacles. Mr. Abbas is a weak leader, representing only the Fatah faction and ruling only the West Bank while the rival Hamas controls Gaza. Mr. Netanyahu heads a hard-line government, and even if he is serious about making peace (the jury is out on that) will his political allies let him? We are encouraged by reports that he wants to participate in the negotiations with Mr. Abbas and that he named a trusted longtime friend as his chief negotiator.

Mr. Obama has set an ambitious one-year timetable for the two sides to settle their longstanding final status issues: borders of a new Palestinian state, security, refugees and the future of Jerusalem. The parameters and the solutions are well known from years of past peace talks. But there is deep mistrust between the parties, and the administration must be willing to point fingers when needed and put forward its own proposals when progress slows.

Mr. Obama will kick the talks off on Wednesday night with a White House dinner attended by Mr. Netanyahu and Mr. Abbas, and by President Hosni Mubarak of Egypt and King Abdullah of Jordan, whose countries have peace treaties with Israel. Tony Blair, the former British prime minister, will represent the United Nations, the United States, the European Union and Russia — the “Quartet” supporting Middle East peace.

That will make for a fine ceremony and important symbolism, but Mr. Obama’s involvement cannot end there. He needs to keep pressing everybody — his dinner guests and other regional leaders, including Saudi Arabia and Turkey — to stand behind peace efforts.

Pessimism about these talks is understandable, given the depressing history of failed peace attempts, but it is no excuse for the leaders not to make a serious effort, and Mr. Obama is right to try to compel them to do that.