THE OBAMA administration has reached an ignominious impasse on Syria. Administration spokesmen now publicly recognize that the United Nations diplomatic initiative it has backed for the past seven weeks has been a failure. They acknowledge — as they should have long ago — that Syrian President Bashar al-Assad has no intention of ending violence against his opposition, or meeting any other condition of the “Annan plan.”

Yet President Obama refuses to embrace other options. His administration’s strategy is one of militant passivity: Officials say they are waiting for U.N. envoy Kofi Annan to agree with them that his diplomacy has failed, and to say so to the U.N. Security Council. They are waiting for the Russian regime of Vladi­mir Putin, which has been pummeling its own pro-democracy movement in the streets of Moscow, to be shamed into abandoning its support for the Assad dictatorship. And they are waiting for the Syrian opposition — which is either in exile or under relentless assault from tanks and artillery — to metamorphose into a coherent alternative with detailed plans for governance.

This strategy will allow Mr. Assad to go on killing indefinitely. Mr. Annan, after all, describes his plan as the only alternative to a Syrian civil war, so he is unlikely to abandon it any time soon. The Russians don’t sound at all shamed: “Things are moving in a positive direction,” Moscow’s U.N. ambassador Vitaly Churkin chirped Tuesday. The Syrian opposition, like any beleaguered resistance to a murderous dictatorship, can be counted on not to reach the high bar set by disdainful desk officers at the State Department.

More than 1,000 men, women and children have died since Susan Rice, the U.S. ambassador to the United Nations, declared the Annan plan “the best way to end the violence.” But the consequences of U.S. passivity go beyond loss of innocent Syrian life. The prolongation of the conflict poses serious threats to U.S. interests and allies.

Three nascent or foreseeable developments stand out. One is that what began as a secular, peaceful and pro-democracy movement in Syria will degenerate into a sectarian war in which the majority Sunni community targets Mr. Assad’s minority Alawites, while Kurds, Christians and other minorities are caught in the middle. In several parts of the country, including the cities of Homs and Hama, that already has happened.

A second danger is that al-Qaeda and other Sunni extremist movements will take advantage of the chaos. As The Post’s Liz Sly recently reported, jihadists have flowed into Syria from Iraq and Jordan, and operatives linked to al-Qaeda are believed to have carried out a series of bombings in the last five months. A double-suicide bombing in Damascus on Thursday was the worst yet.

The third and most grave threat is that sectarian war in Syria will jump across borders. Iraq, Lebanon and Turkey all have the same divides among Shiite and Sunni sects; Iraqi Prime Minister Nouri al-Maliki has said Syria’s fighting could spread “like a house on fire.” Once that happens, outside intervention by the United States would be impossible and the damage uncontainable.

The administration’s experts on Syria recognize the danger. Assistant Secretary of State Jeffrey D. Feltman told the Senate Foreign Relations Committee that “it’s one of the reasons why I said our policy is to try to accelerate the arrival of that tipping point” at which Mr. Assad falls. “The longer this goes on, the higher the risks of long-term sectarian conflict, the higher the risk of extremism. So we want to see this happen earlier,” Mr. Feltman said.

That testimony was delivered on March 1.