Senate Majority Leader Bill Frist (search) on Tuesday delayed potential showdowns with the White House over terrorism detainees and closing U.S. military bases after the Republican-run chamber failed to sidetrack amendments on the two contentious issues.

The Tennessee Republican's decision to put off until fall further consideration of the amendments -- and the $491 billion defense bill they were aimed at -- came after the Senate voted 50-48 to cut off debate on the overall measure. That was short of the 60 votes Frist and the White House needed to prevail.

Under the Senate's rules, a vote to limit debate would have automatically killed the terror-suspect and base-closing amendments. The White House has threatened that President Bush would veto the entire defense bill if the amendments were included in it.

"I'm very disappointed in the last vote," Frist said on the Senate floor. "We will proceed to the bill on gun liability," the next bill on the Senate's schedule.

That provoked outcries from Democrats who accused Frist of pandering to special interests by shelving the defense bill to work on a National Rifle Association-backed bill that would shield gun manufacturers from liability lawsuits.

Congress leaves Washington this weekend for a monthlong summer break.

Talk of legislation regulating the treatment of detainees has percolated on Capitol Hill since last year, when the Abu Ghraib (search) prison abuse scandal in Iraq surfaced. Efforts to craft such legislation gained steam over the past few months amid fresh allegations of abuse and torture at the U.S. detention center at Guantanamo Bay, Cuba (search).

White House lobbying against the proposals intensified late last week. Vice President Dick Cheney met with the three Republicans on Thursday to object.

The administration says it will oppose any restrictions on the president's ability to conduct the war on terrorism and protect Americans.

Democrats have offered their own amendments, including one by Sen. Carl Levin, the top Democrat on Armed Services, that would set up an independent commission to review detention and interrogation practices.

The White House opposes it, and Senate Republicans say they are pushing their detainee legislation in part as an alternative to the creation of such a panel.

"I think it's important to those who want to consider that commission to see that some members are taking very affirmative steps" on the detainee issue, Sen. John Warner, R-Va. told reporters.

An amendment by Sen. John McC (search)ain, R-Ariz., would make interrogation techniques outlined in the Army field manual -- and any future versions of it -- standard for treatment of all detainees in the Defense Department's custody. Warner introduced a watered-down version of McCain's measure that would give the defense secretary the authority to set such rules. But Warner denied bending to White House pressure.

Another McCain amendment would expressly prohibit cruel, inhumane and degrading treatment of prisoners in U.S. custody no matter where they are held.

An amendment by Sen. Lindsey Graham, R-S.C., would define "enemy combatant" and put into law the procedures the Bush administration already has in place for prosecuting detainees at Guantanamo. The amendment would, in effect, provide congressional approval for the Bush administration's legal policies, including those for holding detainees indefinitely.

Also a target of White House ire are amendments by Republican Sen. John Thune of South Dakota, who is trying to save Ellsworth Air Force Base, and a bipartisan group of lawmakers furious over Pentagon plans to close military bases in their states.

The administration says Defense Secretary Donald H. Rumsfeld would recommend a veto if amendments are approved that "weaken, delay or repeal" the base-closing process.

One of Thune's amendments would require the Pentagon to complete several operational reviews and return U.S. troops from Iraq before Congress signs off on the final version of the base-closing plan.

Another would allow Congress to remove bases from the Pentagon's list of proposed closures once those conditions are met. A third would extend whistleblower protections to military members who disagree with the Pentagon's recommendations and want to share that information with the commission reviewing the proposed closures.