Washington ? President Bush’s top foreign-affairs advisers say the United States must be prepared to use nuclear weapons to deter attacks involving weapons of mass destruction. But in an effort to ease alarm overseas, they said there were no plans to do so.

“We all want to make the use of weapons of mass destruction less likely,” national security adviser Condoleezza Rice said Sunday. “The way that you do that is to send a very strong signal to anyone who might try to use weapons of mass destruction against the United States that they’d be met with a devastating response.”

Secretary of State Colin Powell said the United States has never ruled out using nuclear weapons against a nuclear-armed enemy, a policy he said should deter any would-be attacker.

“We think it is best for any potential adversary out there to have uncertainty in his calculus,” Powell said.

Rice, Powell and military and congressional leaders were responding to weekend reports that the Pentagon has told Congress it is studying the possible use of nuclear weapons against countries that threaten the United States.

The classified “nuclear posture review” sent to Congress says the Pentagon is developing contingency plans for using nuclear weapons against countries that are developing weapons of mass destruction.

The report identified seven nations: China, Iran, Iraq, Libya, North Korea, Russia and Syria.

On TV talk shows Sunday, administration officials sought to walk a line between asserting America’s willingness to use nuclear weapons, and calming the public and allies troubled by suggestions the United States might be moving closer to employing them.

Powell said on CBS’ “Face the Nation” that the report emerged from “prudent” planning that must “give some consideration as to the range of options the president should have available to him to deal with those kinds of threats.”

Powell acknowledged the military was considering whether to “modify or update or change” current nuclear weapons to meet new threats.