WASHINGTON (AP) — For 51 years of war and peace, Republicans and Democrats rallied around a bill to pay the troops, buy ships and aircraft and set military policy.

Last week, the Senate couldn't even agree on votes.

Under pressure from President Barack Obama, Senate Majority Leader Harry Reid, D-Nev., was determined to avoid a vote on adding a new batch of tough penalties against Iran to the National Defense Authorization Act as negotiators held nuclear talks in Switzerland. A deal announced Sunday temporarily freezes Iran's nuclear program.

Reid wasn't keen on replaying a fight over the health care law, opening up contentious issues such as government spying or allowing probably the last bill out of Congress this year to become a magnet for other matters.

"Everyone has to understand this is not going to be an open amendment process," Reid told his colleagues as he sought to limit amendments and wrap up the $625 billion defense measure after some three days of debate. He contends GOP delaying tactics have forced his hand.

A power grab, complained frustrated Republicans who demanded they be allowed to offer amendments and get votes on them — the norm for decades on a bill that represents half the nation's discretionary budget.

The GOP repeatedly carps about Reid's heavy-handed control, manifested by the rules change on filibusters. Republicans say the defense bill could have been done months ago but was put off until the last minute to spare Obama a few national security black eyes.

"Republicans are entitled to some amendments," pleaded Sen. Jim Inhofe of Oklahoma, the top Republican on the Senate Armed Services Committee. He offered a whittled list of 25 GOP amendments from the list of 350 put forth by members of both parties.

It was a no go, the latest traditionally bipartisan bill to fall on the hard times of a fractious Congress. In the new normal of congressional inaction, toss the defense bill on the pile with the stalled farm bill, the missing immigration measure and the incomplete individual spending bills.

With just a few legislative days left in the year, the latest machinations leave in jeopardy a bill that authorizes money for personnel, war-fighting equipment and the conflict in Afghanistan. The Senate has to pass its bill and reconcile it with a version the House approved in June.

If the Senate cannot break the impasse when lawmakers return Dec. 9, troops still will get paid and fighter jets will continue to be built thanks to the separate, all-encompassing spending bill. But major policy changes might be lost, including several new measures to stem the epidemic of sexual assaults in the military.

Doing without an authorization bill for the first time in half a century also would represent the fall of one of last bastions of comity in Congress.

"I'm nowhere close to giving up on completing the defense authorization bill, even though we will only have days, not weeks, to complete it," Sen. Carl Levin, chairman of the Armed Services Committee, said in a statement.

Head down and shoulders slumped, Levin looked disheartened by the proceedings on the Senate floor. Elected in 1978, the Michigan Democrats has had two stints as the committee's chairman. He's retiring after next year.

The dysfunction is "approaching an all-time low," said Sen. John McCain, R-Ariz., who like Levin has participated in far more cordial, as well as more open, debates of the defense bill.

In decades past, the leadership often stepped aside and let the chairman and ranking member take charge, debating the bill for hours around-the-clock, allowing numerous Republican and Democratic amendments and plenty of votes.

Arnold Punaro, who worked for former Sen. Sam Nunn, D-Ga., from 1973 to 1997 as a top aide and later staff director of the Armed Services Committee, remembers former Sen. John Tower, R-Texas, keeping senators on the bill for days on end, wrapping up the legislation at 3 a.m.

Amendments were offered, accepted or rejected. Some senators eventually would abandon amendments under the long hours that Tower would make them be there for the debate. The Senate typically spent more than a week on the bill, Monday through Friday and sometimes Saturday rather than the current schedule of Tuesday to Thursday.

"He'd wear 'em down, but he got it done," Punaro said of Tower, who led the committee in the early 1980s.

This past week, the Senate voted on two amendments dealing with the fate of the detention center in Guantanamo Bay, Cuba. Reid sought votes on measures addressing sexual assault in the services after some five hours of debate on Wednesday. Republicans objected as they pressed for other amendments.

"Why have a legislative body if you don't want to debate legislation?" asked Punaro, who bemoaned the curtailing of amendments.

By comparison, the House considered 172 amendments when it debated its version of the defense bill in June. It agreed to 148 of them by voice vote and held 21 recorded votes. Seven amendments were added to the bill through recorded votes over three days of debate and 14 were rejected.

The Senate purposely avoids the time constraints imposed in the House. But votes on just two amendments to the Senate defense bill, plus the measures on sexual assault, before final passage would have been an unusually low number for such a far-reaching measure. Inhofe said that in the past 17 years, the Senate has debated the bill an average of nine days, held an average of 11 roll call votes and adopted nearly 100 amendments by voice vote.

The impasse combined with the brouhaha over how Democrats unilaterally changed the Senate's filibuster rules on Thursday left the Senate's defense stalwarts pessimistic about the road ahead.

"There's a lot of turmoil and I'd like to tell you that the 2014 elections will fix everything," McCain said. "I'm not sure that's the case. I think the problems go deeper than that."