Ten years after the fall of the Berlin Wall, President Clinton said the event was "one of history's most remarkable triumphs of human freedom," but warned that there are many challenges left to "completing the unfinished business of building that stable, unified and democratic Europe."

Clinton, who departs Friday for Europe, laid out what aides called the broad themes of his visit in a speech yesterday at his alma mater, Georgetown University.

He identified three major policy challenges. The first is Russia, which he said is undergoing a transformation that is sometimes "not pretty" but in which the United States has a "profound stake." He urged patience and increased U.S. assistance.

Second, Clinton said Europe's future will pivot around the Balkans, particularly the historically contentious relationship between Greece and Turkey--two countries Clinton will tour. He said he will plead for better relations.

Clinton said the final challenge is at home--whether Americans will stay engaged in international affairs by paying U.N. dues and other costs of leadership. "I think it's worth devoting some small fraction of this nation's great wealth and power to help build a Europe where wars don't happen, where our allies can do their share and we help them to do so."