Mr. Bush said after conferring with Republican House members that he had “reminded them that the most important job of government is to protect the homeland.” As part of his plan, the president wants Congress to enact legislation that would authorize tougher interrogations of suspected terrorists.

Image Senator John W. Warner, the chairman of the Armed Services Committee, speaking to reporters today. Credit... Jamie Rose for The New York Times

And that is what Congress must not do, said Colin L. Powell, the former secretary of state. “The world is beginning to doubt the moral basis of our fight against terrorism,” Mr. Powell said in a letter to Senator John McCain of Arizona, one of the Republicans who differ with Mr. Bush’s policies.

Mr. McCain was one of the four Armed Services Committee Republicans who voted against Mr. Bush’s proposals. The others were Senators John W. Warner of Virginia, the chairman, Lindsey O. Graham of South Carolina and Susan E. Collins of Maine. The measure that the panel endorsed and sent to the Senate floor would let suspects see evidence against them and would bar statements obtained through torture or coercion.

Mr. Powell’s repudiation of the White House’s anti-terrorism approach was both stark and highly unusual for a former cabinet member. In 1980, Cyrus R. Vance resigned as President Jimmy Carter’s secretary of state to protest the failed mission to rescue American embassy personnel held hostage in Iran.

President Bush has contended that a section of the Geneva Conventions that applies to the humane treatment of prisoners is too vague, and that Congress should pass a measure redefining the extent of the United States’ compliance with that section, known as Common Article 3.