President Costis Stephanopoulos formally invited the pope to Greece on Wednesday, during a meeting at the Vatican. Premier Costas Simitis' government endorsed the invitation.
Greece is included on a list of places the 80-year-old pope hopes to visit during his ongoing pilgrimages to biblical sites.
``The leader of the Catholic Church, as a head of state, is always welcome in Greece,'' said ministry spokesman Panos Beglitis.
But Church leader Archbishop Christodoulos said the pope preferred to visit countries ``as the leader of the Roman Catholic Church,'' and not as a head of state.
``For this reason, according to protocol, he must make a request to the church of Greece and then we will discuss it again,'' Christodoulos said.
In November, Greek Orthodox leaders refrained from either approving or disapproving a visit to Greece, suggesting they would not throw up obstacles. But they said the pope must ask them for an invitation if he wanted to come as a church leader.
Other senior clerics, including Christodoulos' spokesman, said they did not favor a papal trip to Athens.
The idea of rapprochement between Roman Catholics and the Orthodox is widely viewed with suspicion and even hostility by the clergy in Greece, who often accuse the Vatican of trying to extend its influence eastward. The Roman Catholic and Eastern Orthodox churches have been divided -- and at odds, sometimes violently -- since the so-called Great Schism of 1054.
The Orthodox Church also has accused the Catholic Church of seeking to steal its members, particularly in parts of the former -- and predominantly Orthodox -- Soviet Union. Another flashpoint has been attempts by the Vatican to reclaim property it owned prior to the communist takeover, and which has since fallen under Orthodox control.
Despite the opposition of the Ukrainian and Russian Orthodox leaders, John Paul II said Thursday he will go ahead with plans to visit Ukraine in June.
He also said he would visit Syria.
The pope's trip to Syria in March or April is an effort to retrace the steps of St. Paul, who converted to Christianity on the road to Damascus. The pope had originally sought to visit Syria in 2000 as part of his Holy Land pilgrimage to Israel, Jordan, Egypt's Sinai Peninsula, and Palestinian-controlled Bethlehem.
The pope referred to the distance between the Catholic and Orthodox at a Christian unity service Thursday at the Vatican before an audience that included representatives of the Russian and Greek Orthodox churches, as well as Anglicans, Lutherans, Methodists and Baptists.
"We cannot and should not diminish the differences that still exist between us," the pope said. "True ecumenical commitment does not seek compromises and makes no concessions on truth. It knows that the separations between Christians is contrary to the will of Christ; it knows that they are scandalous and weakens the voice of the Gospel."