VATICAN CITY - In 26 years of globe-trotting, Pope John Paul II has covered a distance roughly equivalent to three trips to the moon. Yet a longed-for visit to Russia has never come off - and there are doubts that it ever will.

In what could be the twilight of his papacy, a trip to close a centuries-old rift between Roman Catholics and Orthodox Christians appears highly improbable even if John Paul fully recovers from his latest health crisis.

When the 84-year-old pope suffered his first breathing crisis in February, Patriarch Alexy II, the head of Russia's Orthodox Church, sent a warmly worded pledge of "brotherly prayers."

But the influential Orthodox primate remains opposed to the idea of a papal visit, reflecting deep-rooted resentment over perceived Catholic poaching for converts in traditionally Orthodox lands.

Alexy has refused to budge despite the Holy See's return to Orthodox hands of an important icon and the relics of two Orthodox saints. In January, he told The Associated Press that a papal trip would be possible only if the Vatican were to renounce efforts to expand into overwhelmingly Orthodox Russia and the former Soviet republics and proselytize for believers.

The Vatican insists it is merely trying to minister to Russia's small Catholic community - about 600,000 people or less than 1 percent of the country's population of 144 million.

John Paul is widely credited for playing a key role in the collapse of communism across Eastern Europe, most notably in his native Poland, where he threw his support behind the Solidarity trade union.

The pope has been less successful in his efforts to erase a millennium of tension and mistrust between Christianity's two quarreling sisters, who split in the Great Schism of 1054. During a groundbreaking visit to the Vatican in 1989, then-Soviet leader Mikhail Gorbachev invited the pope to visit Moscow, but the timing never seemed right.