The United States' proposed quick-action force might be used not only to react to a military crisis but also to strike first to prevent one, according to President Carter's national security affairs adviser.

The planned 110,000-member Rapid Deployment Force (RDF) has been discussed frequently in recent weeks as the type of military unit the United States needs to react to a crisis such as the one with Iran.

But Zbigniew Brzezinski raised the possibility Tuesday that such a force might be used to avoid such incidents.

"The Rapid Deployment Forces of the United States, which are currently being developed, will give us the capability to respond quickly, effectively and perhaps even preemptively in those parts of the world where our vital interests might be engaged and where there are no permanently stationed American forces," he told the Economic Club of Chicago.

In his speech, Brzezinski did not say what specifically constitutes a vital interest, a threat to which might trigger use of the RDF.

He did say, however, that three "central security zones" -- Western Europe, the Far East and the Middle East -- are of strategic importance to the United States. "The denial of any one of these zones to us would have significantly negative consequences," he said. "And a threat to the security of any one [zone] is an automatic threat to the security of the other two."

In an interview with the Sun-Times, Brzezinski spelled out, in general terms, what type of threat might warrant use of the RDF preemptively or reactively.

He declined to say whether seizure of Middle East oil fields by forces hostile to the United States would automatically precipitate use of the RDF. "We are talking about [hostile invasion] of countries, [blocking] access to resources, [and threats to] certain strategic areas," he said. "It is up to the president to decide, when circumstances dictate it, what action to take."

Brzezinski said the RDF, when fully implemented, would be drawn from troop units stationed in the continental United States. He noted that certain Marine, airborne and other divisions are now available for rapid deployment. But he acknowledged that they cannot be used as effectively now as they could be "a year from now or two years from now or five years from now."