The NATO campaign in Libya to help rebels oust dictator Moammar Gadhafi's murderous regime hardly needs more justification than was evident when the Arab Spring blossomed. The United States' vital support has kept Gadhafi from slaughtering thousands of rebels and civilians, and it continues to be justifiable for that and other reasons. Yet because it directly involves the United States in continuing hostile military actions, it clearly falls under the 1973 War Powers Act.

Under that act, the president is required to seek congressional approval to continue the intervention within 60 to 90 days of onset of hostilities. President Obama should not try to skirt that responsibility.

Given the circumstances, Obama can hardly claim the military campaign is not an act of war. The United States may have no boots on the ground yet, but there's plenty of evidence of deadly engagements by U.S. forces against Libya's regime.

From the beginning, the U.S. military has engaged in bombing of strategic targets - and not just Libya's air defense systems. It has rained hundreds of cruise missiles on military installations. It's also helping refuel NATO planes from France, England and elsewhere, and it is still sending remotely controlled drone aircraft to strike targets.

Yet Obama responded to a recent effort in the U.S. Senate - led by Sen. Bob Corker of Tennessee and Sen. Jim Webb, a Virginia Democrat - to invoke the War Powers Act by pretending that U.S. activities in Libya do not rise to the level of "hostilities" that require compliance with the Act.

His response said 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."

He's fudging, of course. If North Korean fighter jets, for example, were to strike U.S. soil and air defenses and unleash a weeks-long barrage of cruise missiles on strategic U.S. military sites from naval vessels standing off U.S. shores, an American president couldn't say fast enough those actions were acts of war.

The administration's obtuse rebuttal rightly prompted Corker to call for hearings to "examine divergent definitions for 'hostilities' and how this term is used in the legal analysis for continued involvement in the military operations [in Libya] absent specific authorization from Congress."

He makes a crucial point. If the president can say that obvious hostilities are not really "hostilities" as assumed under the War Powers Act - and make it stick - then he not only can upend the War Powers Act with respect to operations in Libya. He also can set a precedent that effectively nullifies the authority of the War Powers Act for future adventures that might lead to a full-on shooting war with troops on the ground.

Corker makes a case that supporters of the Libyan intervention must recognize. If Congress can't make the War Powers Act stick in the event of obvious hostilities, then any president, regardless of political party, can lead the country into war without ever having to justify it, and without Congress having any authority to call the president to account and block the path to full-on war.

Congress must maintain its balance of power over acts of war, and exercise its duty to debate and authorize, or refuse to authorize, continued U.S. involvement in Libya. It must do so as a matter of principle.

There's good reason, of course, to believe that Congress would, in fact, sanction continuing but limited action in Libya. The action began with the endorsement of the United Nations Security Council, with support from some Arab countries, and in cooperation with NATO. England and France have assumed the primary roles, and hawkish Republicans in Congress have demanded even greater involvement. Thus the Libyan campaign has broad support. Retreating from it, moreover, would undermine U.S. influence and credibility.

Congress, and Corker himself, likely would approve a continued, if limited, U.S. role in Libya. But that role should be defined, and the plain definition of hostilities should be respected to keep the War Powers Act intact. Obama should go to Congress and make that case.