When Javier Solana became NATO secretary general four years ago, some of his harshest critics were U.S. congressmen who recalled how the Spanish socialist fought hard--if unsuccessfully--to prevent his country from entering the Western military alliance.

But Solana quickly disarmed his antagonists by asserting his anti-NATO stand was a mild case of "juvenile delinquency." The former physics professor said he had revised his thinking and become a stout proponent of the alliance, observing that "only idiots never change their minds."

As he prepares to leave NATO headquarters this week to take a newly created job as the European Union's head of foreign and defense policy, Solana observed that the alliance, too, has experienced a dramatic transformation in the post-Cold War era.

"The changes have come incredibly fast," Solana said in an hour-long interview Monday. "Just look at Germany. For years, the Germans believed they would never again send troops abroad because of their history. But today, we have a German general who will soon take command over all of NATO's soldiers in Kosovo."

Upon arriving at NATO in December 1995, Solana's first task was to oversee the deployment of of NATO peacekeepers in Bosnia, the first time the alliance ever sent troops outside its domain. He later presided over the incorporation of former Warsaw Pact states Poland, Hungary and the Czech Republic in NATO.

But Solana's biggest accomplishment was his role in preserving NATO's political unity during the 78-day bombing campaign against Yugoslavia earlier this year. Many members were troubled over the legality of NATO's unprecedented attack on another country in the absence of a United Nations mandate.

"There were times when I became really angry," Solana recalled. "I was mad because some countries failed to realize that they can't just take from the alliance, they have to live up to their commitments as well. But in the end, we all saw the need to stick together."

Throughout the air war, Solana won almost unanimous praise for his skill in maintaining consensus among the allies. He believes a large part of his new job will be to resolve potential misunderstandings with the United States as Europe strives to develop a common foreign and security policy. Solana said he is dismayed by the suspicions and skepticism he encountered during recent consultations with U.S. policymakers.

"I realize a lot of people in the United States are very sensitive about what we [in Europe] are trying to do," he said. "If they want to disengage from military responsibilities in Europe, they should go ahead and do it, but they should not use the European initiative as an excuse. I hope we can find ways to calm everybody down."

Solana believes that the alliance may go through some difficult times if the United States builds a ballistic missile defense system while trying to revamp the treaty that banned such systems.

"There is some concern about decoupling [America from Europe] if the U.S. develops this technology," he said. "The big problem will be Russia, because they see this as a threat to their last symbol of equality as a great power."