President Bush hailed exiled Soviet conductor Mstislav Rostropovich as ``a national treasure'' on Wednesday as he welcomed the National Symphony home from its tour of the Soviet Union. ``Your orchestra's long-awaited trip to the Soviet Union reflects the drama of our changing world,'' Bush told Rostropovich at a White House reception. The president noted that Rostropovich had received ``ovation after ovation'' on his just-completed tour of the homeland he had been forced to leave in disgrace in 1974. Bush said the conductor and cello virtuoso had returned ``to a place he never really left'' in the Soviet tour. Rostropovich was stripped of his Soviet citizenship in 1978. He got in trouble with the communist authorities at the time for his vigorous defense of out-of-favor author Alexander Solzhenitsyn. His Soviet citizenship was restored last month and he was given an official apology under political reforms undertaken by Soviet President Mikhail S. Gorbachev. Bush said the conductor of the Washington-based National Symphony was ``inded a national treasure and America is very proud of you.'' Before an audience that included members of the orchestra, Soviet Ambassador Yuri V. Dubinin and industrialist Armand Hammer, Bush said: ``Maestro, you are a true virtuoso, not only of music but of the heart and mind as well.'' Rostropovich then led a string section of 12 cellos in a performance of a work named ``Dodecacelli'' by American composer David Ott.