The United States is talking with NATO allies about possibly invoking the alliance's mutual security agreement, following the devastating terror attacks in New York and Washington.

U.S. officials say the invocation of the mutual-security provision of the NATO treaty would not necessarily mean joint allied operations against the perpetrators of the New York and Washington attacks, but they say it would have strong symbolic meaning and be an important show of support for the United States as it contemplates a response to the worst acts of terrorism on U.S. soil.

Briefing reporters, State Department spokesman Richard Boucher said Secretary of State Colin Powell has conferred by telephone with NATO Secretary-General George Robertson, among others, to talk about a coordinated response to the attacks. "We've been in touch with our mission at NATO," he said, "and the secretary has been in touch with Lord Robertson, indeed about the question of working together with our NATO allies and coordinating with our NATO allies on these matters."

A senior official here said discussion of the mutual-security agreement was initiated by the allies. He said he did not expect it to be invoked, unless and until, it is determined that the U.S. attacks were the work of a foreign terrorist group or government, or combination of the two.

Despite widespread speculation as to who might be responsible for to the attacks, spokesman Boucher said the Bush administration will not be making any public allegations at this point. "We're not pointing fingers," he said. "We're not saying who done it. We're going to do this carefully. We're going to maintain the ability to collect information and not reveal the sources of it."

Mr. Boucher said some 50 U.S. embassies and missions abroad - about one-fourth of the total number - were closed for security reasons following the U-S attacks.

He said the decisions on closures had been left to ambassadors and chiefs of mission in the field, and that there had been no new global alert issued by the State Department.