Mr. Hatch expressed sympathy, but went on to say that “some who say they support our troops turn around and talk about defunding them.

“The message to our troops is that we no longer support them,” he said.

Senator Durbin countered by citing news articles that said some of the new troops being sent to Iraq are going without adequate training or equipment. “Now who is standing behind the troops?” he asked.

Mr. Durbin suggested that Congress revisit the resolution it passed in 2002 authorizing the use of force in Iraq, since the prime reasons cited in it  the threats posed by Saddam Hussein and by weapons of mass destruction that Iraq was thought to possess  were no longer factors.

“By what authority do we continue this war?” he said.

Mr. Specter read the results of a survey of service members conducted by The Military Times, which found that only 35 percent of respondents approved of Mr. Bush’s handling of the war. The senator suggested that in that light, the military might be “appreciative of questions being raised by Congress.”

Mr. Feingold insisted that his resolution would “not hurt our troops in any way” because they would all continue to be paid, supplied, equipped and trained as usual  just not in Iraq.

The panel heard from legal experts, who cited constitutional debates over conflicts ranging from the “quasi-war” with Napoleon in 1798 to peacekeeping missions in Bosnia and Somalia in recent years. No war seemed to hang more heavily over the hearing than Vietnam, where Congress brought American involvement to a close by cutting off financing.

Prof. Robert Turner of the University of Virginia suggested that Congress had made itself responsible for the deaths of the 1.7 million Cambodians estimated to have been slaughtered by the Khmer Rouge, by denying funds for President Nixon to wage war inside Cambodia. Similarly, he said Congress bore responsibility for the deaths of 241 marines killed by a suicide bomber in Lebanon in 1983 because it raised the question of forcing a withdrawal there.