Pentagon officials are reviewing that possibility, and some in Congress agree it needs to be considered.

Bush did not define the wider role he envisions for the military. But in his speech to the nation from New Orleans on Thursday, he alluded to the unmatched ability of federal troops to provide supplies, equipment, communications, transportation and other assets the military lumps under the label of "logistics."

The president called the military "the institution of our government most capable of massive logistical operations on a moment's notice."

At question, however, is how far to push the military role, which by law may not include actions that can be defined as law enforcement — stopping traffic, searching people, seizing property or making arrests. That prohibition is spelled out in the Posse Comitatus Act of 1878, enacted after the Civil War mainly to prevent federal troops from supervising elections in former Confederate states.

Speaking on the Senate floor Thursday, Sen. John Warner, R-Va., chairman of the Armed Services Committee, said, "I believe the time has come that we reflect on the Posse Comitatus Act." He advocated giving the president and the secretary of defense "correct standby authorities" to manage disasters.

Presidents have long been reluctant to deploy U.S. troops domestically, leery of the image of federal troops patrolling in their own country or of embarrassing state and local officials.

The active-duty elements that Bush did send to Louisiana and Mississippi included some Army and Marine Corps helicopters and their crews, plus Navy ships. The main federal ground forces, led by troops of the 82nd Airborne Division from Fort Bragg, N.C., arrived late Saturday, five days after Katrina struck.

They helped with evacuations and performed search-and-rescue missions in flooded portions of New Orleans but did not join in law enforcement operations.

The federal troops were led by Lt. Gen. Russel Honore. The governors commanded their National Guard soldiers, sent from dozens of states.

Defense Secretary Donald Rumsfeld is reviewing a wide range of possible changes in the way the military could be used in domestic emergencies, spokesman Lawrence Di Rita said Friday. He said these included possible changes in the relationship between federal and state military authorities.

Under the existing relationship, a state's governor is chiefly responsible for disaster preparedness and response.

Governors can request assistance from the Federal Emergency Management Agency. If federal armed forces are brought in to help, they do so in support of FEMA, through the U.S. Northern Command, which was established in 2002 as part of a military reorganization after the 9/11 attacks.

Di Rita said Rumsfeld has not made recommendations to Bush, but among the issues he is examining is the viability of the Posse Comitatus Act. Di Rita called it one of the "very archaic laws" from a different era in U.S. history that limits the Pentagon's flexibility in responding to 21st century domestic crises.

Another such law, Di Rita said, is the Civil War-era Insurrection Act, which Bush could have invoked to waive the law enforcement restrictions of the Posse Comitatus Act. That would have enabled him to use either National Guard soldiers or active-duty troops — or both — to quell the looting and other lawlessness that broke out in New Orleans.

The Insurrection Act lets the president call troops into federal action inside the United States whenever "unlawful obstructions, combinations or assemblages — or rebellion against the authority of the United States — make it impracticable to enforce the laws" in any state.

The political problem in Katrina was that Bush would have had to impose federal command over the wishes of two governors — Kathleen Blanco of Louisiana and Haley Barbour of Mississippi — who made it clear they wanted to retain state control.

The last time the Insurrection Act was invoked was in 1992 when it was requested by California Gov. Pete Wilson after the outbreak of race riots in Los Angeles. President George H.W. Bush dispatched about 4,000 soldiers and Marines.

Di Rita cautioned against expecting quick answers to tough questions like whether Congress should define when to trigger the president's authority to send federal troops to take charge of an emergency, regardless of whether a governor agreed.

"Is there a way to define a threshold, or an anti--cipated threshold, above which a different set of relationships would kick in?" Di Rita asked. "That's a good question. It's only been two weeks, so don't expect us to have the answers. But those are the kinds of questions we need to be asking."