As American warplanes carpet-bombed Taliban forces in Afghanistan, Pentagon officials concerned about potential terror threats at home moved toward calling up more reservists than they had planned.

The Pentagon notified the White House that it wants to mobilize more than the 50,000 first thought necessary for the U.S. war against terrorism. It did not offer a new projected total.

"We're not benchmarking it," Pentagon spokeswoman Victoria Clarke said Wednesday.

Clarke also announced that Defense Secretary Donald H. Rumsfeld will leave Friday for Russia and nations near Afghanistan to bolster support for the U.S. bombing campaign.

She would not identify what other cities Rumsfeld will visit except for Moscow, where the secretary plans to talk arms control and anti-terrorism with his counterpart, Defense Minister Sergei Ivanov.

In Wednesday's attacks on Afghanistan, its most intense attacks yet, the United States used B-52 bombers and other warplanes "all over the country, including (against) Taliban forces in the north," said Rear Adm. John Stufflebeem, deputy director of operations for the Joint Chiefs of Staff.

The stepped-up attacks on front line positions came a day after Rumsfeld acknowledged U.S. troops were on the ground in Afghanistan directing bombs to their targets.

During a Pentagon news conference, Stufflebeem said that more than three consecutive weeks of airstrikes have severely damaged the Taliban's communications system to the point that field commanders are having trouble summoning new supplies and troop reinforcements.

"We believe that puts a terrific amount of stress on their military capability," he said.

Stufflebeem said the current focus of U.S. bombing includes bunkers and caves thought to be used by the Taliban and fighters of the Al Qaeda terror network, as well as Taliban troops aligned against opposition forces near the northern crossroads city of Mazar-e-Sharif and just north of Kabul, the Afghan capital.

In explaining why more U.S. reservists are expected to be called to active duty, Pentagon officials said they continue to receive new requests for security forces at federal installations.

Gen. William Kernan, head of the U.S. Joint Forces Command, told reporters he has considered "the full array of air defense systems" to protect some sites.

"Most recently some of the things we looked at are some of the nuclear power plants, some of the other critical infrastructure that supports the national and state governments," he said without elaborating.

Seven states already have put Army National Guard units on security duty at nuclear plants. They are New Jersey, New York, Massachusetts, Connecticut, Arizona, Kansas and Arkansas.

The Air Force has called up more reservists than the other services, 19,643 members of the Air National Guard and Air Force Reserve. They include 5,900 Air National Guard members called up Tuesday.

On Wednesday, an additional 515 Army Reserve and National Guard members were mobilized, along with 208 members of the Naval Reserve. For all the services, just over 42,000 reservists had been called.

Although almost all call-ups have been for domestic defense missions, some are for the conflict in Afghanistan.

Last week, for example, 517 members were activated from the 919th Special Operation Wing based at Duke Field, Fla. That Air Force Reserve unit includes the 711th Special Operations Squadron, which flies the MC-130E Combat Talon used to airdrop special operations troops behind enemy lines, and the 5th Special Operations Squadron, which flies the MC-130P Combat Shadow for similar clandestine missions.