AACHEN, Germany -- President Clinton was honored Friday for his contribution to unity in Europe but German Chancellor Gerhard Schroeder warned him not to destroy that cohesion as he decides whether to deploy an anti-missile defense system.

Clinton, who has already been told by Schroeder that a national missile defense (NMD) could upset the global arms balance, was cautioned by him again after receiving the prestigious Charlemagne Prize in the German border city of Aachen.Schroeder told Clinton--the first U.S. president to receive the award--that although it was the Americans' right to take decisions they need to ensure their security, NMD should be debated with Washington's European partners.

"As this issue could have effects well beyond the USA, it is in the sense of the alliance that it be treated in a spirit of partnership," Schroeder said of NMD which Washington says would shoot down rockets fired by rogue nuclear states.

Russia has warned that the proposed missile defense system could wreck existing arms control pacts.

Clinton, who heads to Russia Saturday and will address the issue in a summit with Russian President Vladimir Putin, did not speak of NMD.

Instead, he focused his comments on the challenges facing Europe--in particular regarding Russia and the Balkans and their integration--and said the United States would continue to support Europe and its unification efforts.

"I believe Europe should want to strengthen our alliance even as you grow stronger," he said. "The alliance has been the bedrock of our security for half a century. It can be the foundation on which our common future is built.

"It's easy to point to our differences; many do. We've always had our differences and being human and imperfect, we always will," he said. "America must remain Europe's good partner and good ally. America has a permanent interest in a permanent alliance with Europe."

Standing in a courtyard on the side of Aachen's 1,000-year old cathedral that houses a shrine to Charlemagne, Clinton said he had done what he could to assist in that effort, but noted there was more to be done.

"Let us keep building this cathedral, the cathedral of European unity, on the foundation of our alliance for freedom," he said to applause from several thousand townspeople who virtually shut down their city for the ceremony.

Apart from his warning on the missile shield, Schroeder heaped praise on Clinton in a long speech detailing the president's efforts to bring about peace and unity in Europe--from Cyprus to Northern Ireland to the Balkans.

"Bill Clinton can look back on his two terms in office with pride," Schroeder said.

"One of his great predecessors, President (John) Kennedy, once won the hearts of all Germans with an unforgettable phrase, when he proclaimed himself to be 'ein Berliner'," he said. "Bill, with your commitment, you have become a European."

In a citation from the city, which was badly damaged by U.S. forces in World War II, Aachen honored Clinton for his action in preserving ethical norms and the rule of law, including the use of military force.

"President Bill Clinton is also being honored for his courageous action--including the use of military means--to preserve rules and ethical norms and the rule of law," it said.

Anger among European pacifists at U.S. military involvement in the continent was voiced by a number of protesters in Aachen against the awarding of the prize.

"No Awards for War!" ran a banner in one health food store window just 100 yards from the square where the ceremony took place. Other shops were decked out in U.S. flags and one displayed a large portrait of Clinton.

Clinton is only the third American--after former secretaries of state George Marshall and Henry Kissinger--to receive the prize, which last year went to British Prime Minister Tony Blair.

The Charlemagne Prize was established in 1949 to recognize the "most meritorious contribution serving European unification and the European community, serving humanity and world peace." Ten previous recipients, including Czech President Vaclav Havel and Spain's King Juan Carlos were on the dais with Clinton.

Later Friday Clinton was to return to Berlin for a dinner with Schroeder and a dozen other world leaders due to attend a conference Saturday on how to reconcile center-left values with the global competition of the "New Economy.