By Ziad Asali and Tom Dine

Joe Biden predicted that Barack Obama would be tested by a foreign-policy crisis early in his term. The recent surge of violence in Gaza came even sooner than that.

How Obama approaches Gaza will be critical not only for the immediate security of Israelis and Palestinians, but also for the resolution of the broader Israeli-Palestinian conflict and U.S. relations with the world's Muslims.

The new cease-fire is unlikely to resolve underlying issues in the conflict. Nor will it be sustainable unless the United States invests substantial political capital in achieving a two-state solution in the next four years.

Doubting voices caution that the new administration and its allies are unlikely to achieve this solution. They point to divided Palestinian leadership, deep political fractures in Israel, strong Iranian and Syrian support for Hamas and Hezbollah, and American leaders' limited ability to motivate Israelis or Palestinians to make the compromises necessary for peace.

The challenges are significant. Nonetheless, we believe that, for the Obama administration, the cost of inaction will be much greater than the cost of trying and not succeeding.

If the United States fails to make a major political investment in reaching the goal, it will undermine moderate Israeli and Palestinian leaders and embolden hard-liners. Even more serious, from the perspective of American security, most of the world's Muslims see the United States not as a neutral mediator but as Israel's key supporter. Rightly or wrongly, they hold it responsible for the continuing conflict.

The longer the United States is perceived as one-sided or inactive in ending the conflict, the more it undercuts its allies across the region and spurs recruiting by al-Qaeda and other extremist groups.

Conversely, evenhanded, sustained efforts by the Obama administration toward a two-state solution will help de-escalate the Israeli-Palestinian conflict, address the injured dignity of Arabs and Muslims, and transform U.S. relations with Muslim countries and people.

The administration must begin by brokering a firm agreement that builds on and goes beyond the fragile cease-fire and the nearly stalled peace process. Palestinian security forces must commit to doing everything in their power (including cooperating with Israeli security and intelligence services) to prevent attacks on Israel. Israeli leaders must make an equally clear commitment to cease settlement construction in the West Bank, support humanitarian relief, and enable Palestinian economic development in the West Bank and Gaza.

The United States has a critical role to play in defining the terms of this agreement, monitoring its implementation, and providing incentives for both sides to stick to it.

The Obama administration will need to address the split in Palestinian leadership. It would be preferable to work with a Palestinian Authority government that includes Hamas, recognizes Israel, and is committed to a nonviolent resolution.

On the other hand, if Hamas remains unwilling to agree to those terms, the United States and its peacemaking partners should work with the Palestinian Authority while using informal and indirect channels (such as via Egypt) to engage with Hamas on a limited agenda of humanitarian and security issues.

The United States, its Quartet partners (the United Nations, European Union and Russia), and moderate leaders in the region also need to deal with the key potential spoilers, Iran and Syria. The United States and others need to create incentives for these states to accept and even support a two-state solution.

In the coming years, the details of the difficult issues of borders, right of return, and Jerusalem will have to be worked out. Accord is possible if each side honors the interim security-settlements agreement, and if complementary measures are taken to improve Palestinians' quality of life and link resolution of the conflict to a wider regional peace agreement.

With presidential commitment from Day One and sustained, skillful diplomacy, a two-state solution may be within reach. Without them, we will likely see grim repetitions of the recent news from Gaza.