The Guardian newspaper, citing unidentified sources, reported Friday that an invitation for Blair and his wife to join the Archbishop of Westminster, Cardinal Cormac Murphy-O'Connor, for lunch at the Venerable English College in Rome was a signal the Roman Catholic church would take Blair into its fold.
According to The Guardian, Blair would be the first serving prime minister to visit the college, founded in 1579 to train priests for England and Wales, where Catholics then faced persecution.
The Vatican press office said Blair would meet with the pope at 11 a.m. (0900 GMT) on Saturday.
Blair's office, citing security considerations, refused to confirm that.
As for reports that Blair is on the verge of formally becoming a Catholic, a spokesman repeated the official line that "he remains a member of the Church of England."
Blair had a previous papal audience with Pope John Paul II in 2003.
Speculation about Blair's religious intentions increased last month when The Times reported that Father Michael Seed - who has shepherded other prominent people into the church - told friends at a recent memorial service that he expected Blair to formally declare his allegiance to the church after he steps down on June 27. However, The Times also quoted Seed as saying he did not know whether Blair would ever be formally received into the church.
The Guardian said that Father John Walsh, a Royal Air Force chaplain, has been an influential figure in Blair's circle for the past four years. Walsh has frequently celebrated Mass for the Blair family at Chequers, the prime minister's official country house, the newspaper said.
Blair is known to be one of the more devout Christians to lead the government in recent decades, though he has been very reticent to discuss his faith. Blair's former spokesman, Alastair Campbell, once cut off a journalist's inquiries with a brusque "we don't do God."
Blair's wife Cherie is a Roman Catholic, the couple's children have attended Catholic schools and Blair habitually attends Catholic rather than Anglican services.
In 1996, a year before he became prime minister, he was admonished by the late Cardinal Basil Hume to stop receiving communion at Mass because he was not a Catholic.
As a student at Oxford University in the 1970s, Blair became acquainted with Peter Thomson, an Anglican priest from Australia who led long conversations with like-minded students about theology and politics, and the idea of community. Blair joined the Church of England at Oxford.
The Act of Settlement of 1700 requires the monarch to be a member of the Church of England and to not marry a Catholic.
However, it has been possible for a Catholic to head the government since 1829, when the Catholic Emancipation Act allowed members of the faith to be elected to Parliament.