WASHINGTON – A rebellious Senate committee defied President Bush on Thursday and approved terror-detainee legislation he has vowed to block, deepening Republican conflict over terrorism and national security in the middle of the election season.

Republican Sen. John Warner of Virginia, normally a Bush supporter, pushed the measure through his Armed Services Committee by a 15-9 vote, with Warner and three other GOP lawmakers joining Democrats. The vote set the stage for a showdown on the Senate floor as early as next week.

In an embarrassment to the White House, Colin Powell – Bush’s first secretary of state – announced his opposition to his old boss’s plan, saying it would hurt the country. Powell’s successor, Secretary of State Condoleezza Rice, jumped to the president’s defense in a letter of her own.

All this played out after Bush started his day by journeying to the Capitol to try nailing down support for his own version of the legislation – and by issuing a threat to the maverick Republicans.

“I will resist any bill that does not enable this program to go forward with legal clarity,” Bush said at the White House.

The president’s measure would go further than the Senate package in allowing classified evidence to be withheld from defendants in terror trials, using coerced testimony and protecting CIA and other U.S. interrogators against prosecution for using methods that may violate the Geneva Conventions.

“The world is beginning to doubt the moral basis of our fight against terrorism,” Powell, a retired general who is also a former chairman of the Joint Chiefs of Staff, wrote in his letter.

Powell said Bush’s bill, by redefining the kind of treatment the Geneva Conventions allow, “would add to those doubts. Furthermore, it would put our own troops at risk.”

Firing back, White House spokesman Tony Snow said Powell was “confused” about the White House plan. Later, Snow said he probably shouldn’t have used that word.

“I know that Colin Powell wants to beat the terrorists, too,” he said.

The administration also produced its own letter from Rice. She wrote that narrowing the standards for detainee treatment as Bush has proposed “would add meaningful definition and clarification to vague terms in the treaties.”

In addition, CIA Director Michael Hayden wrote a letter to his employees saying he has asked Congress “to help define our responsibilities so that we and the Department of Justice can judge the appropriateness of any procedures we would propose to use” while questioning terrorism suspects. He said Bush’s bill did that.

In the committee vote, Warner was supported by GOP Sens. McCain of Arizona, Lindsey Graham of South Carolina and Susan Collins of Maine. Warner, McCain and Graham had been the most active senators opposing Bush’s plan. The vote by the moderate Collins underscored that there might be broad enough GOP support to successfully take on Bush on the floor of the Republican-run Senate.

As the battle mushrooms, it threatens to undermine campaign season assertions by the administration that it has shown a steady hand on security matters and that Republicans should be trusted over Democrats on such issues.

Bush still has many congressional allies, including House and Senate leaders and conservatives, who want to align themselves with the president’s tough stance on interrogation and prosecution. The House Armed Services Committee on Wednesday passed a bill that supports the administration’s position by 52-8.

But that support is not universal. Rep. Steve Buyer, R-Ind., said he told Bush during the president’s visit that he should heed the military’s top uniformed lawyers, who previously have opposed some provisions of the president’s plan.

Buyer and other Republicans are expected to align themselves with McCain, who spent more than five years as a prisoner of war during Vietnam. Last year, he overcame Bush’s objections to pass legislation banning cruel, inhuman or degrading treatment of detainees.

Leaving his closed-door meeting with the House GOP caucus, Bush said he would “continue to work with members of the Congress to get good legislation.” He complimented a House bill but did not mention the Senate version.

“I reminded them that the most important job of government is to protect the homeland,” he said. Bush was accompanied by Vice President Dick Cheney and White House political adviser Karl Rove.

The White House also released a letter to lawmakers signed by the military’s top uniformed lawyers. Saying they wanted to clarify past testimony on Capitol Hill in which they opposed the administration’s plan, the lawyers wrote that they “do not object” to sections of Bush’s proposal for the treatment of detainees.

Two congressional aides who favor McCain’s plan said the military lawyers signed that letter after refusing to endorse an earlier one offered by the Pentagon’s general counsel, William Haynes, that expressed more forceful support for Bush’s plan.

The aides spoke on condition of anonymity because they were not authorized to discuss the matter publicly. Asked if Haynes had encouraged them to write the letter, Pentagon spokesman Bryan Whitman said, “Not that I’m aware of.”

Another Bush bill would give legal status to the administration’s warrantless wiretapping program. The Senate Judiciary Committee approved the bill on a party-line vote Wednesday, but it is stalled in the House amid opposition from Democrats and some Republicans concerned that the program violates civil liberties.

AP writers Robert Burns and Katherine Shrader contributed to this report.