U.S. lawmakers question the legality of President Barack Obama's continued use of the U.S. military in Libya without the approval of Congress. U.S. House of Representatives Speaker John Boehner, the top Republican in Congress, last week said Congress could cut funding for U.S. military involvement in Libya, ratcheting up pressure on Obama.
Gates, who departs as Pentagon chief this month after serving in the post under one Democratic and one Republican president, noted that earlier during his stint in the job Congress also threatened to cut off funding for the Iraq war.
"Frankly, I think cutting off funding in the middle of a military operation when we have people engaged is always a mistake," Gates told "Fox News Sunday."
Speaking on the CNN's "State of the Union," Gates predicted a positive outcome of the NATO-led campaign in Libya.
"We are seeing the Gaddafi government weaken," Gates said. "... I think this is going to end OK. I think Gaddafi will eventually fall."
Gates added "my own bet" is that Gaddafi "will not step down voluntarily, but somebody will make that decision for him -- either his military or his family." Asked whether that meant someone would kill Gaddafi, Gates said, "Possibly."
He said he could not make a prediction on how long it would take before Gaddafi falls.
The New York Times reported in its Saturday editions that Obama rejected the views of top lawyers at the Pentagon and the Justice Department when he decided he had the legal authority to continue U.S. military involvement in Libya without congressional authorization.
The Times reported that key Pentagon and Justice Department lawyers concluded that the U.S. operations in Libya amounted to "hostilities." Under a U.S. law known as the War Powers Resolution, such a determination would have required Obama to end or scale back the mission after May 20, according to the Times.
That law was enacted in 1973 during the Vietnam War era.
The law prohibits U.S. armed forces from being involved in military actions for over 60 days without congressional authorization, with a 30-day pullout period. Boehner says these 90 days are up on Sunday.
Gates declined to offer his personal view on the question of "hostilities," saying, "I'm going to defer to the White House and to the president on the legal interpretations."
But he said, "I was in the White House and the NSC (National Security Council) staff not long after the War Powers Act was passed. And I believe that President Obama has complied with the law, consistent in a manner with virtually all of his predecessors. I don't think he's breaking any new ground here."
"I think he's been clear, as well, that he would welcome the Congress passing a resolution of support," Gates added.
NATO is leading the effort whose stated mission is to protect Libyan civilians from Gaddafi's forces -- a mission whose unstated goal seems to be to drive the Libyan leader from power -- with the U.S. providing logistical support and intelligence.
Criticism of the Libyan conflict has been fueled by general unease in both U.S. political parties over a third war after Afghanistan and Iraq, and worries about more costs in a time of massive debt. There is also an element of partisan criticism of a Democratic president from Republican lawmakers including some like Representatives Michele Bachmann and Ron Paul who are seeking their party's nomination for president in 2012.