As the Roman Catholic Church's first diplomatic representative to Russia in nearly two centuries, Archbishop Francesco Colasuonno has been at the forefront of an unprecedented dialogue between the Vatican and the world's biggest Orthodox nation.


When Colasuonno departs this weekend for a new posting in Rome, the Italian prelate said he will be leaving with "mixed feelings," but at a time when relations "are improving" with the Russian Orthodox Church, which has had a historically stormy relationship with the Vatican.


Colasuonno, 69, said he feels privileged, as the highest ranking Catholic in Russia, to have taken part in the reunification of Russia's 300,000 Roman Catholics with their church.


"It has been a wonderful experience to see the church become conscious of its liberty," he said in an interview, "for the good of its souls."


In his new position, he will be the Pope's representative to the Italian government, considered the best posting in the Vatican's diplomatic corps.


Four and a half years ago, after former Soviet President Mikhail Gorbachev's historic visit to Pope John Paul II, Colasuonno was appointed the Papal Nuncio -- the Pope's representative in Moscow, but not a full-blown ambassador.


He was the first such envoy since 1803.


"I am, so to speak, an appendix to the diplomatic list," said Colasuonno, whose successor has not been appointed.


"Since it has worked well, I think that in a few years the mission status will be upgraded to the dignity" of an embassy.


In his tenure in Russia, delegations from the Vatican have met on a regular basis with the Russian Orthodox Church, discussing issues ranging from the restitution of former church property to the primacy of the Pope -- a point of contention since the schism between the Western and Eastern Christian churches in 1054.


As a diplomat, Colasuonno can be circumspect about tensions between the two churches. But a Russian priest who edits a monthly Russian-language Catholic magazine characterized the current relationship as "not terribly good."


Father Alexander Khmelnitsky, the editor of Istina i Zhizn, said a low point came in April 1991, when the Vatican appointed two bishops to serve in Russia.


"It was taken as an attempt to expand into their territory," said Khmelnitsky, referring to the Orthodox. "They are very irritated as the Catholic church in Russia becomes more and more Russian."


Khmelnitsky called the doctrinal differences between the two churches "practically insignificant to the ordinary believer" -- but in practice, he said, this does little to smooth relations.


"Peculiarly, the Orthodox are more obsessed with the Catholics than with the Protestants -- probably because we are so close to each other," said Khmelnitsky.


The overwhelming dominance of the Orthodox Church in Russia has given Russian Catholics a flavor of their own, one that Colasuonno said should be savored.


Catholics in Russia "show a characteristic of mysticism, because the Russian soul tends to be more mystical, as it is practiced in the Orthodox church," said Colasuonno.