THE OBAMA administration’s depiction of its Libya venture as too halfhearted to be covered by the War Powers Resolution contains an unfortunately large dollop of truth. President Obama’s commitment is sufficiently halfhearted to undermine the NATO alliance. It is sufficiently halfhearted, and confused in its statement of purpose and its connection of ends to means, to give Moammar Gaddafi hope that he can hang on. It is not, however, so halfhearted as to justify the administration’s evasion of its legal duties under the war powers law.

That law is deeply flawed. It infringes on the president’s prerogative to command the military free of undue and unrealistic constraints. Every president since it was passed under Richard M. Nixon has chafed under its obligations, and none has fully bowed to its demands, but none has formally challenged its constitutionality, either. It is the law of the land.

So what is Mr. Obama’s rationale for flouting it? The resolution requires the president to obtain congressional approval for armed interventions within 60 days of their initiation and to wind down hostilities within 30 additional days if such approval isn’t forthcoming. Under those terms, Mr. Obama needed to obtain congressional approval by May 19 to keep U.S. forces in the Libyan campaign. The administration has missed the deadline by a month; it recently agreed to stay with the NATO-led operation until Sept. 27 — some seven months after the fight began.

The administration argued in a report to Congress released this week that it need not seek approval because the operations in Libya “are distinct from the kind of ‘hostilities’ contemplated” by the War Powers Act. “U.S. operations do not involve sustained fighting or active exchanges of fire with hostile forces, nor do they involve the presence of U.S. ground troops, U.S. casualties or a serious threat thereof, or any significant chance of escalation into a conflict characterized by those factors,” the report states.

Problem is, the War Powers Act does not define “hostilities” as requiring boots on the ground or exchanges with hostile forces. The act, in fact, does not define hostilities, leaving a vacuum that Mr. Obama and his predecessors have exploited in self-serving ways. We believe that an honest appraisal of the activities that the United States continues to engage in would put the administration squarely within the purview of the War Powers Resolution. By the administration’s own account, these include airstrikes aimed at “suppress[ing] enemy air defense,” “occasional strikes by unmanned Predator” drones, and intelligence and logistical support that aid other NATO members in carrying out their strikes.

We supported Mr. Obama’s decision to join NATO allies in the U.N.- sanctioned effort to keep Libyan strongman Gaddafi from slaughtering his people. The president is right to sustain the effort until a regime less dangerous to its own people is installed, and he would be wise to heed U.S. allies and join in the effort more robustly. But it strikes us as fatuous to argue that the United States is not engaged in hostilities, given that the NATO bombing campaign could not be taking place without active U.S. support.

Mr. Obama is not the first president to pretend to comply while skirting the law’s most important provision, but precedent does not make the practice more appealing.