The U.S. needs a new, modern arsenal of nuclear weapons to use as a deterrent to attacks from other nations for the remainder of the 21st century, the top military commander for strategic warfare said Tuesday.

Air Force Gen. Kevin Chilton, head of the military's Strategic Command, said if the Pentagon develops an improved, more reliable nuclear weapon, the U.S. will be able to reduce the number of warheads it keeps on hand.

"So long as there are other countries in the world that possess enough nuclear weapons to destroy the United States of America and our way of life, we will have to deter those types of countries," Chilton told reporters at a breakfast meeting. "So I am not in favor of unilateral disarmament."

Comparing today's threat to the Cold War, when the U.S. was at loggerheads with the Soviets, Chilton said the principle deterrent was the "massive nuclear threat of destroying each other's countries."

Now, he said, the threat is different, thus the deterrent must also be more nuanced — ranging from nuclear warheads to conventional weapons and cyber-capabilities. And he said the existing warheads in the U.S. inventory today are "too big, bigger than they need to be."

Critics, however, worry that any such moves by the United States could trigger another international arms race, and a rush by other countries — such as Russia and China — to develop more effective, more usable nuclear weapons.

"This is something we should be very careful about — the signal we send to other nuclear powers in the world," said Hans M. Kristensen, director of the Nuclear Information Project for the Federation of American Scientists. "We don't want Russia and China to make more usable and tailored weapons capabilities."

Kristensen said members of Congress have already expressed concerns that developing weapons with lower yields would make them more usable.

"It's a good thing that we have weapons that are not very usable," he said. "The worst situation would be where they are more likely to be used."

Chilton noted that the United States has significantly reduced the number of nuclear weapons it now has in its active arsenal. By 2012, he said, the number would be reduced to about one-quarter of the total during the Cold War.

The 2002 Moscow treaty requires that the U.S. reduce its operationally deployed warheads to 1,700-2,220 by December 2012. In an exchange of data early last year, the Russians claimed to have 4,162 strategic warheads and the United States 5,866 in its arsenal.

Chilton said the military can use as a deterrent either a large stockpile or a more modern, responsive weapon in smaller numbers. And he advocated the latter, saying that would be a smarter way to reduce the nuclear inventory.

At the same time, he acknowledged that the warheads are powerful and terrible weapons.

"I'm a father too, with children, and I would love to have them grow up in a nuclear-free world," Chilton said. "But ... I also want them to grow up free. And as long as we have other nations out there with nuclear capabilities ... then we need to have a nuclear deterrent force that can do the mission of preserving our freedoms."