President Obama has set clear and appropriate priorities ahead of the visit to Washington on May 18 by Prime Minister Benjamin Netanyahu of Israel. Speaking to Jewish-American activists last week, Vice President Joseph Biden conceded, “You’re not going to like my saying this,” and then he laid out the administration’s list.

If there is going to be a serious peace effort with Palestinians, Israel must work toward a two-state solution, Mr. Biden said. It must freeze further settlement construction in the West Bank and dismantle roadblocks between Palestinian cities and towns not needed for security. Israel must also grant Palestinians more responsibility for security to the extent that they combat extremists and dampen incitement against Israel, he added.

This should not come as news to Mr. Netanyahu. Mr. Obama and his aides have been telegraphing their intentions for weeks. But the Israeli leader’s responses have been unconvincing and insufficient. Growing tensions were obvious when his White House meeting slid later into May — after Mr. Obama hosted Arab leaders.

In his video speech to the same activist group, the American Israel Public Affairs Committee, Mr. Netanyahu said he wants peace with the Palestinians. He even committed to negotiations “without any delay and without any preconditions.” But it rings hollow. He has resisted — and his foreign minister and unity government partner, Avigdor Lieberman, has openly derided — the two-state solution that is the only sensible basis for a lasting settlement that could anchor a regional peace. On Monday, the 15-member United Nations Security Council unanimously adopted a statement endorsing the two-state solution.

Other differences also threaten next week’s meeting. One is the president’s decision to reach out to Iran, which has made Israel uneasy. Mr. Netanyahu — perhaps trying to ensure talks with the Palestinians never get anywhere — hinted that he might condition peace efforts on Mr. Obama’s success in ending Tehran’s nuclear program.

Stopping Iran’s nuclear program is crucial. Mr. Obama’s approach — a serious diplomatic overture followed by tougher sanctions if talks fail — is risky but worth it. Yes, the clock is ticking as Tehran’s capability improves. But Mr. Netanyahu should not artificially constrain Mr. Obama’s initiative. And Mr. Obama must discourage any move by Mr. Netanyahu to lead Israel, or push the United States, into unnecessary military action.

It cannot be either-or. We have seen how former President George W. Bush’s delay in engaging seriously on Israeli-Palestinian peace efforts sabotaged United States interests in Afghanistan, Pakistan, Iraq and Iran by giving Al Qaeda and other extremists a rallying point for anti-Americanism. There are huge obstacles to peacemaking, including the rivalry between the ruling Fatah and militant Hamas Palestinian factions. Fortunately, there is also a new, potentially useful dynamic: Arab states like Saudi Arabia and Egypt are as worried about Iran as Israel is. That is a shared concern that should be exploited to bind these old adversaries in common cause — to advance Israeli-Palestinian peace and to restrain Iran.

As new leaders of two deeply entwined countries, President Obama and Mr. Netanyahu have an interest in getting their relationship off to a good start. Mr. Netanyahu, a smooth talker, will have to do better than vague promises, however. Just think what might happen if he declared an end to settlement construction and an early return to substantive final status negotiations.

Mr. Obama could then challenge Arab leaders who supported a 2002 peace initiative to respond, perhaps by initiating openly acknowledged diplomatic contacts and trade ties with Israel. Pessimism is the norm in the Middle East, but those kinds of moves could be game-changers.