IT WOULD be wrong to dismiss a potential move by Syria to place its chemical weapons arsenal under international supervision — a possibility that suddenly appeared Monday when a seemingly offhand comment by Secretary of State John F. Kerry was seized upon by Russia.

But it also would be foolish to forget how the regime of Bashar al-Assad has used previous diplomatic proposals to stall and sandbag international intervention while continuing to wage a merciless war against its population. If this initiative works, it will happen only because the regime and its patrons in Moscow are made to believe that the alternative is a devastating U.S. military strike.

In tossing out the idea at a London news conference, Mr. Kerry said Mr. Assad “could turn over every single bit of his chemical weapons to the international community in the next week” before predicting that “he isn’t about to do it, and it can’t be done.” That was a realistic assessment both of Mr. Assad — who has never made a promise he did not break — and of the potential difficulty of establishing international control over stockpiles scattered across Syria, including at military bases that are crucial to the regime’s war-fighting.

Mr. Kerry’s idea — gaffe, some said — was taken up within hours by Russia’s foreign minister, who said Syria should not only place its chemical weapons under international control but also agree to their eventual destruction by signing the treaty that bans them. Soon the U.N.secretary general, the British prime minister and some in Congress had embraced the idea, which the Syrian foreign minister said he “welcomes.” And no wonder: A monitoring plan not only would spare Damascus a U.S. strike that could tip the balance in its civil war but could also allow for endless dickering. Who will the inspectors be? How will they be protected on Syrian military bases? Will the United States be asked to forswear any intervention in the war in exchange?

It’s worth remembering that when the United Nations attempted to broker a deal in March 2012, envoy Kofi Annan announced that Mr. Assad had accepted a six-point peace plan, including a cease-fire with U.N. monitors. Syrian forces were to pull back from urban areas, allow humanitarian assistance and begin releasing prisoners. Not one of those terms was respected. Government forces continued their bloody siege of cities such as Homs and Hama. Unable to carry out their mission, the monitors withdrew, and Mr. Annan resigned.

There’s only one reason an initiative on chemical weapons might turn out differently: a credible threat of military action by the United States. That makes Congress’s vote on a resolution authorizing force all the more important. If the resolution is approved, the administration will have leverage to push through the Russian proposal. If one or both houses of Congress reject the authorization, the Assad regime can be expected to find a way to reject the deal or dodge compliance indefinitely.

Meanwhile, the civil war will go on. Moscow and Damascus may calculate that the Assad regime has a better chance of surviving if both chemical weapons and the possibility of U.S. intervention are taken off the table. But the regime’s prolongation would be a disaster for Syria and U.S. interests in the Middle East. That’s why, whatever the outcome of the chemical-weapons initiative, Mr. Obama should keep his promise to step up support for Syrian rebels.