RUSSIA AND the United States have pursued dramatically different strategies on Ukraine in the 10 days preceding a diplomatic meeting Thursday in Geneva. While loudly denouncing what it has described as direct Russian intervention in eastern Ukraine and threatening tough sanctions, the Obama administration elected not to take any concrete action in the hope that the meeting, which also includes the foreign ministers of Ukraine and the European Union, will produce positive results. The administration also has refused Ukraine’s desperate requests for non-lethal aid for its military as it attempts to turn back the quasi-covert offensive.

Russian President Vladi­mir Putin, in contrast, clearly is unconcerned about provoking the other side. Russian operatives, who apparently have infiltrated military forces, have been steadily stepping up their attacks on Ukrainian government installations in a dozen or more cities and towns. On Wednesday these forces and their Ukrainian followers managed to turn back a weak effort by the Ukrainian government to retake some of the installations, in one case disarming a column of government soldiers and confiscating their armored personnel carriers.

Consequently, Russian Foreign Minister Sergei Lavrov will arrive in Geneva with considerable leverage. With eastern Ukraine in Russian-induced chaos, Moscow is ready not to negotiate but to dictate terms. “Ukraine,” said Mr. Lavrov on Wednesday, “must be forced to start genuine rather than cosmetic constitutional reform.” By that he means Ukraine should be forced to dismember itself into autonomous regions that the Kremlin could manipulate and ultimately control.

What chips do the United States and European Union have to counter Moscow’s bald aggression? Little more than vague threats. “We are actively looking at our options,” said White House spokesman Jay Carney on Tuesday. Officials privately say they are working with the Europeans on a modest expansion of last month’s sanctions against Mr. Putin’s inner circle — while holding off on the far-more-potent “sectoral sanctions” that Mr. Kerry said were “on the table” last week.

The Obama administration is not wrong to pursue a diplomatic solution to the Ukraine crisis. But diplomacy can’t succeed when the underlying balance of forces is lopsidedly in favor of a U.S. adversary — and the administration declines to take actions that might create incentives for compromise. That’s as true of Mr. Putin’s Russia as it is of Bashar al-Assad’s Syria, which dismissed the last U.S. effort to broker an accord in Geneva after Mr. Obama elected not to provide significant support for Syrian rebels.

Administration advocates of inaction argue that Washington should move only in concert with European governments, which have much larger economic interests in Russia and consequently are more reluctant. But as it demonstrated with Iran, the United States has the power to take potent action on its own, especially in the financial sector — and such steps can induce other countries to join in. By waiting for Europe, the Obama administration essentially hands a veto over its response to what it describes as unacceptable transgressions to states such as Cyprus and Malta.

The Obama administration’s attempt to smooth the way for a diplomatic solution has virtually ensured that the Geneva meeting will fail. Once it does, the president should take action that will give Mr. Putin tangible cause to pull back.