Are there really more than 64 million U.S. Roman Catholics?

That's what the 2007 "Official Catholic Directory" reported.

But what about the dead, the double-counted and the disgruntled ex-Catholics — all of whose names may still plump up parish rolls?

Yes, there are probably "ghosts" on the Catholic lists, says demographer Mary Gautier, senior researcher for the Center for Applied Research in the Apostolate, in Washington, D.C. The center analyzes data for the U.S. Conference of Catholic Bishops.

CARA's analysis counts 64.4 million Catholics in 2006, up from 63.9 million in 2005. (The directory's overall totals are higher because they include Puerto Rico, Guam and American protectorates.)

Totals are up, with minor fluctuations — 1 percent a year for the past 25 years, Gautier says. "But counting Catholics is more art than science."

Catholics drift from parish to parish without ever formally moving their membership. Heirs neglect to tell parish secretaries that Mom or Dad has died.

And those who have stopped going to church or switched denominations rarely bother to formally quit, she says.

The American Religious Identification Survey in 2001 counted almost 51 million Catholics in the U.S., making them the nation's largest denomination. ARIS found that nearly 9.5 million Americans consider themselves ex-Catholics.

However, they are counterbalanced by the millions who still consider themselves Catholic but are not officially counted because they've never registered or they were baptized in another country, says Gautier. She's a co-author of "American Catholics Today," an analysis published this spring of Gallup surveys from 1987 to 2005.

Those surveys "get a substantially larger number who say they are Catholic than the directory counts."

They find Catholics still cling to their religious identity no matter how far they stray from church.

"Still, that's all extrapolation, and demographers don't love extrapolations," says Gautier. So the "Official Catholic Directory" and CARA statistics stick with parish registration, baptismal rolls and sometimes the subjective estimate of the diocesan bishops who submit the numbers.

The accuracy depends on whether the lists are "cleaned" with any regularity. It's an issue worldwide.

The technology magazine Wired recently touted a Web site for the Italian Union of Rationalists and Agnostics that claims 30,000 Italians have downloaded copies of a formal procedure, drawn from a Vatican Web site, for removing their names from the institutional church head count.

Although no one knows how many global Catholics have discovered the forms and mailed exit letters to their priests, "we see a traffic spike every time the pope says something unpopular," site manager Raffaele Carcano told "Wired."

No, they're not getting unbaptized. It's impossible.

"You may not practice, you may not believe. You may not belong to a parish. But technically, you're always a Catholic," says Monsignor Michael Servinsky, a canon law expert and the vicar general for the Diocese of Altoona-Johnstown, Pa.

"We used to get letters all the time from Jehovah's Witnesses asking to be taken off the baptismal registry, but we never did it because you can't be unbaptized. We did make note in the registry and stop counting them as practicing Catholics," says Servinsky.