Vice-President Dick Cheney is working to kill the amendments that Republican Senators John McCain and Lindsey Graham want to tack on to a bill setting Defence Department policy for next year.
McCain, a former prisoner of war in Vietnam, and Graham, who spent 20 years as an Air Force lawyer, introduced the legislation on Monday. Republican John Warner, chairman of the Senate Armed Services Committee, has endorsed the effort.
"What we're trying to do here is make sure there are clear and exact standards set for interrogation of prisoners," McCain said on the Senate floor. "To fight terrorism, we must obtain intelligence, but we have to ensure that it's reliable and acquired in a way that's humane."
Senate aides, who spoke on condition of anonymity because they were not authorised to let their names be used, said the measures were not toned down even though White House lobbying against them intensified late last week.
Cheney met the three Republican lawmakers just off the Senate floor for about 30 minutes on Thursday evening.
Talk of legislation started after
the Abu Ghraib scandal surfaced
That followed an administration statement that President George Bush's advisers would recommend a veto of the overall bill if amendments were added that restricted the president's ability to conduct the "war on terror" and protect Americans.
Senate aides estimate that nearly a dozen Republicans could be on board - which would be more than enough for the amendments to pass. Democrats, who have long criticised the administration for the treatment of detainees, are supportive.
Talk of legislation regulating US treatment of terrorist suspects has percolated on Capitol Hill since last year when the Abu Ghraib prison abuse scandal in Iraq surfaced.
But the effort by leading Republicans to standardise treatment of terrorist suspects has gained steam over the past few months.
Criticism by human rights groups and lawmakers over the military's detainee camp in Guantanamo Bay, Cuba, reached a fever pitch this spring amid fresh allegations of abuse and torture there.
One of McCain's amendments would make interrogation techniques outlined in the US Army field manual - and any future versions of it - the standard for treatment of all detainees in the Defence Department's custody.
"What we're trying to do here is make sure there are clear and exact standards set for interrogation of prisoners"
US Republican senator
The US also would have to register all detainees in Defence Department facilities with the Red Cross to ensure all are accounted for.
Another McCain amendment would expressly prohibit cruel, inhumane and degrading treatment of prisoners in US custody no matter where they are held.
The Vietnam veteran also supports a pair of amendments Democrats are likely to sponsor prohibiting the US from exporting terrorist suspects to countries that are known to torture prisoners, and requiring the US to register with the Red Cross detainees held outside of Defence Department facilities.