WASHINGTON (AP) — Congress is rethinking the broad authority it gave the president to wage a war on terror after the Sept. 11, 2001, terrorist attacks in light of how President Barack Obama has used the power to target suspected terrorists with lethal drone strikes.

Senior Pentagon officials insisted on Thursday that the law should remain unchanged as the nation remains locked in armed conflict with al-Qaida and its affiliates, a fight that will rage for another decade or two. But Republicans and Democrats fear that they have given the president a blank check for using military force worldwide.

"This authority ... has grown way out of proportions and is no longer applicable to the conditions that prevailed, that motivated the United States Congress to pass the authorization for the use of military force that we did in 2001," Sen. John McCain, R-Ariz., said during a Senate hearing. He told Pentagon officials that "basically you've got carte blanche as to what you are doing throughout the world."

Michael Sheehan, assistant secretary of defense for special operations and low-intensity conflict, told the Senate Armed Services Committee that for the war against al-Qaida, the Taliban and other terrorist groups, the 2001 Authorization for the Use of Military Force "serves its purpose."

"I believe that al-Qaida, although its narrative ... is very powerful among certain groups. Ultimately it will end up on the ash heap of history, as with other groups ... but that day, unfortunately, is a long way off," Sheehan said.

Several senators, including McCain, Armed Services Committee Chairman Carl Levin, D-Mich., Lindsey Graham, R-S.C., Dick Durbin, D-Ill., and Bob Corker, R-Tenn., met privately recently to discuss revising the law. McCain indicated at the hearing Thursday that they could act on the annual defense policy bill expected this summer or produce a new resolution.

Durbin, the No. 2 Democrat in the Senate, summed up the frustration of many in Congress who backed the law in 2001 but now wonder whether they went too far as the nation reeled from the shock of the attacks.

"I don't believe many, if any, of us believed when we voted for that — and I did vote for it — that we were voting for the longest war in the history of the United States and putting a stamp of approval on a war policy against terrorism that, 10 years-plus later, we're still using," Durbin said.

Days after the attacks on the World Trade Center and Pentagon, Congress enacted the Authorization for the Use of Military Force.

The law gave President George W. Bush the authority to launch the invasion of Afghanistan and target al-Qaida, saying the commander in chief has the authority to attack "nations, organizations or persons he determines planned, authorized, committed or aided the terrorist attacks that occurred on Sept. 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons."

Emerging threats beyond the borders of Afghanistan and the president's use of drone strikes have raised questions about the relevance of a law nearly 12 years later.

The issue came to the forefront earlier this year as Sen. Rand Paul, R-Ky., waged a nearly 13-hour filibuster of John Brennan's nomination for CIA director over the president's authority to use drones in the United States. The Senate eventually confirmed Brennan.

The president has promised to explain his drone policy, but members of Congress argue that he has been less than forthcoming about the secret program, the existence of which the government only publicly acknowledged last year.

The administration has never publicly described the effectiveness of the program. However, independent groups, relying on news reports and other information, have compiled estimates on the attacks. The New America Foundation, a Washington-based think tank, estimates the U.S. has launched 420 strikes in Pakistan and Yemen — the two countries where the strikes are believed to occur most frequently — since 2004. Between 2,424 and 3,967 people are believed to have been killed by U.S. drones, the majority in Pakistan.

Three Americans were killed in strikes in Yemen in 2011. The target of the first strike was U.S.-born al-Qaida leader Anwar al-Awlaki. American Samir Khan, an al-Qaida propagandist, was killed in the same attack, and al-Awlaki's son, Abdulrahman, was killed the following month.

McCain pressed Robert Taylor, the Pentagon's acting general counsel, whether the law gives the administration the authority to use lethal force against al-Qaida associates if they are identified in Mali, Libya and Syria. Taylor said the United States has the authority.

Sen. Joe Donnelly, D-Ind., questioned the Pentagon officials about how the United States would treat the extremist group Jabhat al-Nusra, one of the most powerful and effective rebel groups in Syria battling the regime of President Bashar Assad. The group, which the United States has designated a terrorist organization, has pledged its allegiance to al-Qaida.

Sheehan said the threshold would be an organized force affiliated with al-Qaida that has threated the U.S.

The testimony prompted incredulity from Sen. Angus King, I-Maine.

"I've only been here five months, but this is the most astounding and most astoundingly disturbing hearing that I've been to since I've been here," King told the witnesses. "You guys have essentially rewritten the Constitution here today. The Constitution Article I, Section 8, Clause 11 clearly says that the Congress has the power to declare war."

King complained that the administration was reading the authority of the law to "cover everything and anything."