Defense Secretary William S. Cohen told the NATO allies today that the United States believes it may soon be necessary to develop a missile defense system to counter threats from "rogue states" with ballistic weapons, but insisted it would be done with allied security interests in mind.

Seeking to convince skeptical European governments, Cohen said the United States and its allies must start to consider how to cope with new challenges, besides the nuclear arsenals of Russia and China, that will soon include long-range missiles being developed by North Korea, Iran and Iraq that could deliver nuclear, biological or chemical warheads.

"It is important for our allies to understand that the threat [from rogue states] is real, that it will intensify in coming years, and that it will put their own populations and their own forces at risk," Cohen told reporters after a meeting of NATO defense ministers.

President Clinton is not expected to make a final decision on a national missile defense before next summer at the earliest. Cohen reassured the allies that the system would take into account their security interests. But NATO's new secretary general, George Robertson of Britain, said the European allies have already raised "a number of profound questions" about the system's potential impact on the alliance.

The missile defense system has sparked deep concern among European countries who fear that it could lead to the abrogation of the 1972 Anti-Ballistic Missile Treaty the United States signed with Russia that is regarded as a foundation of nuclear arms control. Russia has refused to alter the treaty, which prohibits both countries from developing missile defense systems.

Making a detailed case for a missile defense system for the first time at alliance headquarters, Cohen explained that NATO will face a variety of evolving threats over the next 15 years that will dramatically transform the monolithic strategic landscape it confronted in staving off a Soviet invasion during the Cold War.

He said the United States was willing to provide its European allies with a missile defense system that would provide the same kind of protection as sought by the United States. But there was no indication today that any European government was willing to sign up for such a program.

But Cohen stressed to the Western allies that they could not avoid the consequences of such a threat. He cited a study by the National Intelligence Council claiming the proliferation of medium-range ballistic missiles, driven mainly by exports from North Korea, "has created an immediate, serious and growing threat to U.S. forces, interests and allies, and has significantly altered the strategic balances in the Middle East and Asia."

The declassified U.S. study noted that within five years North Korea may develop the Taepodong II as an intercontinental ballistic missile that would be capable of delivering a payload of several hundred kilograms--enough for early generation nuclear weapons--and could strike anywhere in the United States or Europe.

The study also says Iran is working on a long-range missile that, within 10 years, could be capable of striking the United States, Canada or Europe. Iraq may achieve the same capability by 2015, although it may require substantial foreign assistance to do so, the report says.

While acknowledging that Cohen made a compelling case, several European ministers said they were not persuaded that the advantages of a missile defense system outweighed the risks. German Defense Minister Rudolf Scharping noted the proposed timing of Clinton's decision was troubling because it would come in the middle of Russia's presidential election campaign and could fuel support for anti-Western nationalists there.

French Defense Minister Alain Richard expressed doubts that the U.S. missile defense plan would represent a net gain in Western security because it would require enormous investments that could be better spent on other military projects. He also warned about provoking Russia and China into retaliating with new measures such as missiles tipped with multiple warheads designed to overwhelm such defenses.

"We must be very cautious about a program that could end up damaging our security if it offers indirect encouragement to an arms race," Richard said.

Apart from the dangers of an escalating arms race through a profusion of nuclear warheads and other countermeasures, Britain and France harbor concerns that their own small nuclear deterrent forces could be rendered ineffective if other nations respond to the American system by developing antimissile defenses of their own.