The Obama administration argued Wednesday that its nearly three-month-old military involvement in Libya does not require congressional approval because of the supporting role most U.S. forces are playing there, a position that puts it at odds with some Republican leaders and the antiwar wing of its own party.

The White House reasoning, included in a 32-page report to Congress, is the administration’s first detailed response to complaints from lawmakers of both parties, who say President Obama has exceeded his authority as commander in chief by waging war in Libya without congressional authorization.

The report came on the same day a bipartisan group of lawmakers filed suit in federal court against Obama seeking to end the U.S. participation in Libya, pushing what has been a slow-moving confrontation over the power of the president at a time of war toward the center of the political debate.

What began as a complaint from those mostly on the partisan fringes of Congress has attracted more lawmakers with each passing week of the Libya operation, which the Obama administration has said is making significant progress in forcing Libyan leader Moammar Gaddafi from power. In issuing the report, the White House relented in joining a debate it has largely tried to ignore.

The demand that Obama secure congressional approval to continue the Libya operation has brought together House Republicans and liberal Democrats. Some lawmakers have raised the legal question in the hope of stopping the war on principle, while others view the argument as a useful partisan critique of the president’s leadership.

The report is unlikely, as a result, to appease all congressional leaders concerned about Obama’s strategy in Libya and the rising cost of the war, one of three the administration is fighting at a time of severe fiscal strain at home.

The United States has spent $715.9 million in Libya, the vast majority of it on military operations, according to the report. The administration estimates that the cost will rise to $1.1 billion through September, although it does not plan to request additional funds from Congress to pay for the mission.

The report also says that “there has not been a significant operational impact on United States activities in Iraq and Afghanistan” as a result of the Libya campaign.

On the legal question, which the report spends a single paragraph addressing, the administration states that Obama believes he has participated in the Libya operation in a way “consistent” with the War Powers Resolution, passed by Congress in 1973 in an attempt to constrain a president’s war-making capabilities after the undeclared conflicts in Vietnam and Korea.

The report says that “because U.S. military operations [in Libya] are distinct from the kind of ‘hostilities’ contemplated by the resolution,” the deadlines for congressional approval or force withdrawal do not apply.

“We’re not engaged in sustained fighting. There’s been no exchange of fire with hostile forces. We don’t have troops on the ground. We don’t risk casualties to those troops,” said one senior administration official, who briefed reporters on the condition of anonymity during a conference call arranged by the White House. “None of the factors, frankly, speaking more broadly, has risked the sort of escalation that Congress was concerned would impinge on its war-making power.”

Under the War Powers Resolution, a president has 60 days from the start of military operations to obtain congressional authorization or withdraw forces from the fight.

In the case of Libya, that deadline expired last month with the Obama administration failing to do either. The House voted June 3 to give Obama two weeks to comply with the resolution, a deadline that expires Friday.

In a letter to Obama on Tuesday, House Speaker John A. Boehner (R-Ohio) wrote that “the ongoing, deeply divisive debate originated with a lack of genuine consultation prior to commencement of operations and has been further exacerbated by the lack of visibility and leadership from you and your administration.”

At the heart of the administration’s argument is the nature of the U.S. role in Libya, which has changed since Obama announced March 19 the start of operations meant to protect Libyan civilians from forces loyal to Gaddafi, who had threatened reprisals against the residents of the rebellious city of Benghazi.

After taking the lead in destroying Gaddafi’s air-defense capabilities in the early days, U.S. military commanders turned over day-to-day control of the operation to NATO. Obama declared at the start that no U.S. forces would serve on the ground in Libya, and he has maintained that position.

The bulk of the U.S. mission now involves providing aerial surveillance, targeting information, refueling capabilities, and other support for British, French and other NATO-member warplanes carrying out most of the airstrikes.

Obama also approved the use of armed drones in Libya. But the senior administration officials who briefed reporters Wednesday said the aircraft are a minor part of what is mostly a support operation.

“The creative arguments made by the White House raise a number of questions that must be further explored,” Brendan Buck, Boehner’s spokesman, said in a statement. “Regardless, the Commander-in-Chief has a responsibility to articulate how U.S. military action is vital to our national security and consistent with American policy goals.”

Buck said, “We will review the information that was provided today, but hope and expect that this will serve as the beginning, not the end, of the president’s explanation for continued American operations in Libya.”

The War Powers Resolution has been ignored frequently by past presidents from both parties.

But Obama, a former lecturer in constitutional law, came to office pledging a strict adherence to the rule of law, which he accused the George W. Bush administration of violating, most notably in its detention and interrogation policies.

White House press secretary Jay Carney said Wednesday that he did not know whether Obama personally believes the law is constitutional, even though as a candidate he asserted that wars fought with congressional approval were more legally sound.

“I would point out that there has been some expressions on the Hill about this issue that are inconsistent with expressions in the past about the constitutionality of the War Powers Resolution,” Carney said.

Jules Lobel, a professor at the University of Pittsburgh School of Law who has written extensively on the issue, said the administration is “definitely supporting hostilities in a context where they could be fired upon.’

“They are involved in a war, and the fact that they are in a support role, that I don’t think is dispositive in the War Powers Resolution debate,” he said.

Staff writer Felicia Sonmez also contributed to this story.