More active-duty troops are joining the Hurricane Katrina relief effort than originally planned, and a senior commander said Monday they likely will be needed for months, not weeks.

Although the Pentagon said Saturday that 2,500 soldiers from the Army's 82nd Airborne Division (search) were being dispatched to the New Orleans area, a spokeswoman for the division said Monday that 4,700 would be there by Tuesday.

Also going are combat and support forces from the 1st Cavalry Division (search) and 13th Corps Support Command (search) at Fort Hood, Texas, plus about 2,000 Marines. The Pentagon originally said the 1st Cavalry was sending 2,700 soldiers, but division spokesman Capt. George Lewis said Monday that 1,700 were going, plus 100 support troops.

Thus the total for active-duty ground forces would be about 8,500, up from the 7,200 announced on Saturday.

Twenty-one Navy ships also are participating, including the aircraft carrier USS Harry S. Truman (search) off the coast of Mississippi.

The Air Force said Monday that its aircraft have flown more than 1,000 missions, including helicopter crews that have rescued more than 3,600 people and evacuation flights that have moved 2,600 medical patients.

Navy Adm. Timothy Keating, commander of U.S. Northern Command which is responsible for military support to civilian authorities during domestic emergencies, told reporters at the Pentagon that in addition to the active-duty troops, there are about 38,000 National Guard troops in Louisiana and Mississippi. As commanders arrive on the scene of the disaster, some are requesting additional support from their home bases, he said.

"I'm not surprised the numbers are swelling just a little bit," Keating said in a telephone interview from his headquarters at Peterson Air Force Base, Colo. He said he had toured the devastation with Defense Secretary Donald H. Rumsfeld and Gen. Richard Myers, chairman of the Joint Chiefs of Staff, on Sunday.

Keating acknowledged that the federal response to Katrina could have been better, and he said there would be a post-disaster analysis to draw lessons from the experience. But he insisted that efforts were under way even before the hurricane reached land on Aug. 29. "Aid was moving before the storm hit," he said.

It's too early to predict how long active-duty troops will be needed in Louisiana and Mississippi, Keating said, but he said it appears "we'll be there a relatively long time -- I would see it in months, not weeks."

Maj. Amy Hannah, spokeswoman for the 82nd Airborne, said in a telephone interview from New Orleans that search and rescue of the stranded was the top priority, working with the 45th Infantry Brigade of the Oklahoma Army National Guard. She said Maj. Gen. William B. Caldwell IV, the commander of the 82nd Airborne, had been designated the commander in charge of all federal military forces operating in Louisiana.

Hannah said the search-and-rescue mission in New Orleans has been dubbed Operation Waal, recalling the 82nd Airborne's bloody Waal River crossing (search) in Holland in September 1944.

Keating, meanwhile, said his command is not letting the tragedy on the Gulf Coast divert its attention from terrorism. He did not mention any specific threats, but he said, "We're watching the terrorism situation in our headquarters very carefully."