IN HIS first trip as secretary of state, John F. Kerry has been raising expectations that the Obama administration will soon take new action to help the Syrian opposition. President Obama, he said Monday in London, “is currently evaluating precisely what steps we will take in order to . . . lead on this important issue.” He added: “We are determined that the Syrian opposition is not going to be dangling in the wind, wondering where the support is or if it’s coming.”

Mr. Kerry spoke those words because he had to. Rebel leaders, fed up with America’s refusal to supply the weapons, money and training they need to accomplish the stated U.S. goal of ending the regime of Bashar al-Assad, were threatening to skip a “Friends of Syria” meeting in Rome on Thursday. But Mr. Kerry’s promises also set up an important test of credibility for him, and for the president. If the administration now fails to move decisively to break Syria’s bloody stalemate, it could lose what may be a last chance to partner with the more moderate forces challenging Mr. Assad and to steer the country toward a new regime that the West could support.

What could those steps be? A State Department adviser on Syria during Mr. Obama’s first term, Frederick C. Hof, offered a good outline in a recent paper for the Atlantic Council. The United States, he said, should build “close working relationships” with “carefully vetted elements of the Free Syrian Army.” That means, at the least, providing training, tactical intelligence and nonlethal equipment; we believe that heavy weapons are also essential. So far U.S. policy has been to refuse all aid to such groups — a practice that, as Mr. Hof puts it, ignores the reality that “men with weapons will be very influential in charting Syria’s future.”

U.S. policy must also aim at helping the rebels establish a full-fledged alternative government on Syrian territory and recognizing it as the legal government of Syria. That would legitimize the supply of arms and allow the U.S. military to protect the Syrian population with airstrikes or Patriot anti-missile batteries, if that were necessary to stop the regime’s unconscionable targeting of civilian neighborhoods with missiles and artillery. It could also help to marginalize the growing al-Qaeda presence in rebel forces.

The Post reported Wednesday that the administration is considering the supply of nonlethal equipment to rebel forces, a measure Britain and France have already decided on. But in public, Mr. Kerry has spoken only of increased aid to the opposition Syrian National Coalition — which also has yet to receive direct U.S. aid. The Post has reported that new supplies of weapons are reaching rebels in southern Syria, probably with financing from Saudi Arabia and coordination by the United States. This is the extension of an operation that has been underway for some time, but it is too small to quickly decide the war.

Mr. Kerry still speaks of seeking “a political solution,” though the hope of brokering a deal between the regime and the rebels proved illusory long ago. He says that he aims to “change the calculation on the ground for President Assad,” as if it were still conceivable that this blood-drenched butcher could be induced to quietly step down. And Mr. Kerry is still seeking the cooperation of Russia in ending the war, though Vladi­mir Putin has made it clear that his first purpose in Syria is preventing a U.S.-engineered regime change.

Such tactics are doomed to failure. They will serve only to prolong and intensify the bloodshed, to the ultimate benefit of al-Qaeda and those, such as Iran’s leaders, who would prefer endless civil war to any change of government. If the Obama administration is to lead on Syria, it must commit itself to steps that can bring about the early collapse of the regime and its replacement by a representative and responsible alternative. Only direct political and military intervention on the side of the opposition can make that happen.