President Obama missed a legal deadline Friday — set in a 1973 law — that required him to obtain congressional approval for U.S. military operations in Libya.

Friday was the 60th day since Obama formally notified Congress that U.S. planes would strike targets in Libya, a bid to protect civilians from the government of strongman Moammar Gaddafi. Under the Nixon-era War Powers Resolution, the president must obtain congressional authorization of military action within 60 days or else begin withdrawing forces.

Neither happened. Instead, in a letter sent Friday night to congressional leaders, Obama expressed support for a proposed resolution that “would confirm that Congress supports the U.S. mission in Libya.”

The president also described U.S. military efforts as “supporting” and “more limited” than in the campaign’s early days. He said they include providing logistical and intelligence help to the NATO-led operation, as well as supplying aircraft and unmanned drones to attack Libyan targets.

Obama did not, however, explicitly say whether he thinks the War Powers Resolution applies to the Libyan operation. That act makes no specific exception for limited or supporting action: It applies to any instance in which military forces are “introduced into hostilities,” or sent into foreign territory or airspace while equipped for combat.

Congressional leaders have showed little desire to challenge Obama on the deadline. Presidents Ronald Reagan and Bill Clinton also had not obtained congressional approval for overseas actions, with little repercussion from Capitol Hill.

After Obama sent his letter, Jon Summers, a spokesman for Senate Majority Leader Harry M. Reid (D-Nev.), said only that “Senator Reid has received the letter and is giving it his full consideration.”

An aide to House Speaker John A. Boehner (R-Ohio) said the lawmaker had not seen the draft resolution that Obama mentioned. “No decisions will be made until such a review takes place and we discuss the matter with our members,” Michael Steel wrote in an e-mail.

But the resolution has not been formally introduced, said a spokeswoman for Sen. John McCain (R-Ariz.), one of a group of senators whom Obama cited as its sponsors. Brooke Buchanan said the current draft expresses general support for the operation in Libya and contains no mention of the War Powers Resolution.

Legal scholars say that congressional inaction could severely weaken a law intended to take back legislative control of U.S. warmaking.

“The fundamental point is: Before we engage in a serious military endeavor, both branches should give their consent,” said Bruce Ackerman, a Yale University law professor. If Obama ignores the law, he said, “we go back to the status quo before 1973. I mean, Richard Nixon will have won.

The War Powers Resolution was an attempt to settle a dispute as old as the Constitution. That document says only Congress has the power to declare war but the president is commander in chief of the military.

Presidents construed that to mean they could send U.S. forces into combat without congressional approval. In many cases, the reasoning was that the fights would be too small, or too short, to be considered a “war.”

In 1973, Congress tried to take back its power. But almost since the War Powers Resolution was written, presidents have been trying to ignore it. Many have argued that it is unconstitutional, usurping presidential powers to command.

In 1982, Reagan sent Marines into Lebanon and kept them there for a year without official congressional approval. Congress finally passed a resolution authorizing him to continue for 18 more months.

In 1999, during the conflict in Kosovo, Clinton authorized U.S. airstrikes on Yugoslavia. The 60-day deadline passed, with no explicit permission from Congress (although lawmakers did provide funding for the strikes). The air campaign ended after 78 days.

The Libyan conflict is the resolution’s first major test since then. Previously, Obama had indicated that he might abide by the rules: On March 21, he sent Congress a notice, consistent with the act, saying that U.S. forces were joining attacks on Libya.

As the deadline drew closer, six Republican senators sent Obama a letter asking whether he intended to comply with the act. Last month, four House Democrats made similar inquiries.

Next week, the House Foreign Affairs Committee will hold a hearing on war powers and the U.S. operations in Libya. A spokesman for Sen. Richard G. Lugar (R-Ind.) said the senator will ask about it during a nomination hearing for a State Department official.

But so far, the leaders of both parties in the House and Senate have said little about enforcing the deadline.

That makes for a rare moment on Capitol Hill — because these Republican and Democratic leaders rarely agree on anything, and because all lawmakers usually don’t want to surrender power to the executive branch.

But Jules Lobel, a University of Pittsburgh law professor, said that lawmakers, like those in past Congresses, appear to see little upside in interfering with a military operation.

“If you authorize it, and it turns out badly, you’re on the line. And if you refuse to authorize it, the president then says, ‘We’re weak, and it’s because Congress is weak,’ ” said Lobel, who represented a group of congressmen who unsuccessfully sued Clinton for ignoring the law in 1999. “So they say, ‘Do what you want; we’re not going to take responsibility.’ ”

Staff writer Perry Bacon Jr. contributed to this report.