Bush said aggressive action would be needed to prevent a potentially disastrous U.S. outbreak of the disease that is sweeping through Asian poultry and which experts fear could mutate to pass between humans. Such a deadly event would raise difficult questions, such as how a quarantine might be enforced, the president said.

The Posse Comitatus Act of 1878 bans the military from participating in police-type activity on U.S. soil. But Dr. Irwin Redlener, associate dean of Columbia University's Mailman School of Public Health and director of its National Center for Disaster Preparedness, told The Associated Press the president's suggestion was dangerous. Giving the military a law enforcement role would be an "extraordinarily Draconian measure" that would be unnecessary if the nation had built the capability for rapid vaccine production, ensured a large supply of anti-virals like Tamiflu and not allowed the degradation of the public health system. "The translation of this is martial law in the United States," Redlener said.

And Gene Healy, a senior editor at the conservative Cato Institute, said Bush would risk undermining "a fundamental principle of American law" by tinkering with the act, which does not hinder the military's ability to respond to a crisis. "What it does is set a high bar for the use of federal troops in a policing role," he wrote in a commentary on the group's Web site. "That reflects America's traditional distrust of using standing armies to enforce order at home, a distrust that's well-justified."

Healy said soldiers are not trained as police officers, and putting them in a civilian law enforcement role "can result in serious collateral damage to American life and liberty."