WASHINGTON (AP) -- The Democratic-controlled Senate turned back a Republican-led effort Thursday to bar Sept. 11 terror suspects from being prosecuted in civilian federal courts.

Instead, senators voted 54-45 to support a request by Defense Secretary Robert Gates and Attorney General Eric Holder to have the option of prosecuting Sept. 11 terror suspects such as accused mastermind Khalid Sheikh Mohammed in either federal courts or by a military commission.

The vote capped an impassioned substantive Senate debate between those who believe the Sept. 11 terrorists simply do not belong in civilian courtrooms and those who say deciding where to prosecute them should be left to the best judgment of the Pentagon and the Justice Department.

Opponents noted that the government prosecuted 195 terrorists in civilian courts since the terror attacks of Sept. 11, 2001, with a 91 percent conviction record, and only three terrorists have been tried before military tribunals.

Republican Sen. Lindsey Graham led the drive to require those accused of plotting the attacks to be tried in military courts. He said it is wrong to treat the assaults as a criminal act instead of an act of war and that Sept. 11 terrorists do not deserve the same constitutional rights as U.S. citizens.

Supporters of Graham said trials have disclosed intelligence that proved useful Al Qaeda. The trial of Omar Abdel-Rahman, the blind Egyptian sheik convicted of plotting in the 1990s to blow up New York landmarks, revealed a list of co-conspirators that made its way to Osama bin Laden.

"What happened in the blind sheik trial?" Graham said. "Because it was a civilian court built around trying common criminals, the court didn't have the protections military commissions will have to protect this nation's secrets and classified information."

Democratic opponents of the idea said U.S. courts have processed far more terrorists than military ones and that the decision of where to prosecute the terrorists is best made by the Pentagon and Justice departments working in collaboration.

"Our courts and our criminal justice system can handle this challenge, indeed, has handled it many times already," said the Judiciary Committee chairman, Democratic Sen. Patrick Leahy. "We're the most powerful nation on Earth. We're the most tested court system on Earth. Are we going to tell the world with all our power, with all of our history ... we're not up to trying people?"

Five of the accused Sept. 11 plotters are being held at the Guantanamo Bay, Cuba, detention facility, which the Obama administration is struggling to close.

Gates and Holder weighed in last week against Graham's amendment, saying the two agencies are "engaged in a careful case-by-case evaluation of Guantanamo detainees."

They also said in a letter to Senate leaders that the United States "must be in a position to use every instrument of national power, including both courts and military commissions, to ensure that terrorists are brought to justice."

Graham's amendment was co-sponsored by Sens. Joe Lieberman, an independent, and Republican John McCain.