Zalmay Khalilzad was the U.S. permanent representative to the United Nations from 2007 to 2009 during the George W. Bush administration.

The United States has a window to facilitate an orderly transition in Syria without deploying military force. But the window is narrowing — and the Obama administration will need to adjust its political strategy to succeed.

Diplomatically, the administration has focused on engaging the U.N. Security Council and the Friends of Syria, a French-created group of 88 participating states, seven international organizations and one observer (the Vatican). But the Security Council remains in stalemate by Russian and Chinese vetoes, and the Friends of Syria is too unwieldy to reach agreement on operational measures that would change conditions on the ground.

Militarily, the administration’s decision to provide only non-lethal assistance to the Syrian opposition is prolonging unfavorable trends on the battlefield. While opposition gains have precluded the possibility of President Bashar al-Assad shooting his way to victory, the opposition is too weak to bring the conflict to an end. Beyond exacerbating the human toll, a long civil war increases the likelihood that state institutions will fragment, that weapons of mass destruction will be used or fall into the wrong hands, that extremists — such as fundamentalist Salafi Islamists and al-Qaeda — will make headway, and that ethnic and sectarian bloodletting will go on after the Assad regime falls.

To facilitate an orderly transition without deploying force, the United States must do five things:

First, galvanize a “coalition of the relevant”: a select group of like-minded countries that have significant leverage and influence in Syria. While continuing to engage the United Nations, the Friends of Syria and NATO, Washington should focus on integrating efforts with Turkey, Saudi Arabia, Jordan, Qatar and other Gulf states, as well as Britain and France.

Second, President Obama should appoint a special envoy to work with the coalition in organizing the Syrian opposition into a broad-based front that provides a vehicle for a stable transition, attracts support from Syrians fearful of regime change, and co-opts elements of the Assad regime. Chaos and an Iraq-style bloodbath — in which Syria’s Alawite minority, embittered at the loss of their privileged position, turns to insurgency while Sunnis, empowered after decades of repression, seek revenge — are possible.

Regional powers have been unable to unify the opposition or identify credible leaders who enjoy broad national support. The Syrian National Council is disproportionately composed of exiles and members of the Muslim Brotherhood whose following among Syrians and stated commitments to an inclusive Syria are untested. The Free Syrian Army is more in tune with realities on the ground, but it remains unclear how unified that group is and whether the paramilitary force can govern responsibly once the fighting ends. The Kurds’ loyalty to the Syrian state is fraying. And the Alawite-dominated military is tainted by long-standing loyalties to the Assad dynasty.

While democratic consolidation should be the guiding objective, Washington may face unpalatable options in the short term, such as an ethnic and sectarian war or a coup by military officers willing to come to terms with the opposition and reform the state. To reduce the risk of civil war, the administration should work with moderate elements of the opposition to appeal to Syria’s Alawites, Christians, Kurds and other minorities, which would further fracture the regime’s support. It should seek to rally these forces around the principles of democracy, pluralism, decentralized rule and respect for universal rights. Working with the opposition, the United States should encourage a military coup that would be a way station to full democratization while preserving key state institutions. Should such a coup occur, Washington should insist that defectors commit to reforming key ministries and facilitating the transition to democracy.

Third, Washington should end the apparent division of labor that gives regional powers the lead in arming the opposition. The United States needs a seat at the table. Military support provides the leverage necessary to shape a united front politically. Direct U.S. involvement improves the likelihood that arms are distributed to Syrians who embrace a moderate and inclusive order, which would tilt the balance of power away from sectarian and Islamist groups.

Fourth, as conditions change, Washington should seek an understanding with Moscow. Russia and Iran have alienated much of Syrian society in supporting Assad, jeopardizing their long-term interests in Syria. Yet they will accommodate an orderly transition only if it becomes clear that Assad’s downfall is imminent and that unqualified support for Assad and other holdouts is a losing strategy. The coalition should ease Russia’s shift in policy by reassuring Moscow that its core strategic and business interests can be protected in a new Syria. In exchange, Russia should be expected to refrain from vetoing U.S.-backed Security Council resolutions, to cease all support to the Assad regime and to pressure Bashar al-Assad in Syria.

Iran, as the principal backer of Assad, will be more difficult to woo. Given the risk of a backlash against allies and sectarian brethren in the regime, Tehran may shift to a two-track policy: abandon Assad, engage the opposition and support the political transition while providing assistance to the remnants of Assad’s regime. Iran plays a similar game throughout the region. Consolidating a political transition that enjoys broad Syrian support would leave Tehran with little choice but to accommodate the new order or strain relations with a government already reeling from decades of Iranian support for the Assad regime.

Fifth, Washington should remain open to an active U.N. role in finalizing a transitional road map once the conditions for a new order are in place. The United Nations has played such a role in post-Taliban Afghanistan, among other places, where U.N. special representatives catalyzed a process to establish an interim regime, draft a constitution and hold elections.

The time has come for greater U.S. engagement in Syria. By forging a coalition of the relevant, Washington can facilitate a political transition that ends the bloodshed, precludes an array of crises — from terrorism to proliferation of weapons of mass destruction — and lays the groundwork for a stable, democratic Syria.