The panel voted 15-9 to back the bill, which Mr Bush has vowed to block.
Ex-Secretary of State Colin Powell has backed Republicans opposing legislation sponsored by Mr Bush that would allow military tribunals at Guantanamo Bay.
Correspondents say the split within the party risks damaging its prospects in November’s mid-term elections.
Four Republican senators joined opposition Democrats on the Armed Services Committee to approve their measure instead of the tougher bill put forward by the president.
“The world is beginning to doubt the moral basis of our fight against terrorism,” said former Sec. of State Colin Powell
The senators argued that Mr Bush’s proposals would effectively redefine the Geneva Conventions to allow harsh treatment of detainees held at the Guantanamo Bay camp in Cuba.
Bush’s request to give the Executive branch unlimited powers and to “re-define” the Geneva convention has met with opposition from his own party. Chief among them is former Sec. of State Colin Powell who has the respect of MANY moderate republicans and democrats alike.
Once again we wonder what this guy smokes at night before he goes to bed! With less than a month and a half before the mid term elections once again GW manages to alienate members within his own party! Not the sharpest tack in the draw. But hey, we all figured that one out already.