McHale stressed that the response units will be subject to the act, that only 8 percent of their personnel will be responsible for security and that their duties will be to protect the force, not other law enforcement. For decades, the military has assigned larger units to respond to civil disturbances, such as during the Los Angeles riot in 1992.

U.S. forces are already under heavy strain, however. The first reaction force is built around the Army's 3rd Infantry Division's 1st Brigade Combat Team, which returned in April after 15 months in Iraq. The team includes operations, aviation and medical task forces that are to be ready to deploy at home or overseas within 48 hours, with units specializing in chemical decontamination, bomb disposal, emergency care and logistics.

The one-year domestic mission, however, does not replace the brigade's next scheduled combat deployment in 2010. The brigade may get additional time in the United States to rest and regroup, compared with other combat units, but it may also face more training and operational requirements depending on its homeland security assignments.

Renuart said the Pentagon is accounting for the strain of fighting two wars, and the need for troops to spend time with their families. "We want to make sure the parameters are right for Iraq and Afghanistan," he said. The 1st Brigade's soldiers "will have some very aggressive training, but will also be home for much of that."

Although some Pentagon leaders initially expected to build the next two response units around combat teams, they are likely to be drawn mainly from reserves and the National Guard, such as the 218th Maneuver Enhancement Brigade from South Carolina, which returned in May after more than a year in Afghanistan.

Now that Pentagon strategy gives new priority to homeland security and calls for heavier reliance on the Guard and reserves, McHale said, Washington has to figure out how to pay for it.

"It's one thing to decide upon a course of action, and it's something else to make it happen," he said. "It's time to put our money where our mouth is."