"Right of Return" would flood Israel with millions of Arabs.
Cardinal Renato Martino, head of the Vatican department that formulates refugee policy, made the comment as U.S. President George W. Bush was set to revive long-stalled Israeli-Palestinian peace talks at a White House summit.
"Palestinian refugees, like all other refugees, have a right to right to return to their homeland," Martino said in response to a question about the 44-nation conference in Annapolis on Tuesday.
Martino did not make clear whether he meant refugees had a right to return to homes in what is now Israel or to an eventual Palestinian state.
Prime Minister Ehud Olmert and Palestinian President Mahmoud Abbas have
pledged to try to forge a peace treaty by the end of 2008 that would create a Palestinian state.
The issue of the return of Palestinian refugees, along with the status of Jerusalem, is one of the most sticky issues in a peace treaty.
There are some 4.5 million Palestinian refugees in camps in Syria, Lebanon, Jordan, the West Bank and the Gaza Strip.
Successive Israeli governments have made clear they will not accept the right of return of Palestinians who left homes in what is now Israel, saying it would threaten the country's existence.
Some ministers have said that some Palestinians might be allowed to settle in Israel on humanitarian grounds if a final peace settlement is reached.
The Vatican, which sent a delegation to Annapolis, supports a Palestinian homeland as well Israel's right to exist in security.