Blair, who is currently Anglican, had decided to seek admission to the Catholic Church, according to unidentified sources in London and Rome.
Blair is due to step down as prime minister next Wednesday, handing over power to Chancellor Gordon Brown.
A spokesman for Blair declined to comment.
"There are matters of personal belief which I don't deal with," the spokesman said.
"The prime minister wishes ... to talk to the pope, as he has done in the past, about not just inter-faith issues, but also global and regional issues, and one of those obviously is the situation in the Middle East," he said.
Blair's spokesman further noted that a Vatican source has said Blair plans to travel to Rome to see the pope on Saturday, but said nothing about any conversion plans.
Blair is believed to have taken communion from the late Pope John Paul during a visit to the Vatican in 2003, although the Vatican has never confirmed this.
Mr Blair has been attending Catholic services for many years, and regularly worshipped at the 5.30pm Saturday evening service at Westminster cathedral until security considerations persuaded him to seek a private arrangement.
He turned to Father Michael Seed, a familiar and gregarious figure in Westminster who prepared the Conservative MPs, John Gummer and Ann Widdecombe, for conversion.
Father Seed became a regular visitor to Number 10, but sources say Blair cast around about four years ago for a less well-known, and more discreet, spiritual counsellor.
