But such statements effectively let individuals decide whether to receive Communion, and Archbishop O'Malley has specifically said he wouldn't refuse the sacrament to Kerry.

St. Louis Archbishop Raymond Burke, however, said just before the Missouri primary that he would not serve Communion if Kerry came to him at the altar.

"Catholic bishops have the right to deny John Kerry Communion," McGreevy acknowledges, but it's a "terrible mistake" to do so because Catholic politicians face such complex decisions.

The Rev. Thomas Reese of America magazine says Communion bans could make abortion seem a matter of Catholic doctrine rather than general human rights. And author-columnist Peter Steinfels warns that a hard line could make American Catholics imitate Europeans' "nonchalant anticlericalism, that just brushes off church teachings in public affairs."

Without raising the Communion issue, other bishops have denounced pro-choice Catholic politicians, either in general or by name (Indiana Gov. Joe Kernan, New Jersey Gov. James McGreevey). And Senate Minority Leader Tom Daschle's bishop asked him to remove mention of Catholic membership in campaign literature.

Democrats and liberals note that George W. Bush's policies violate bishops' pronouncements on many matters. But Catholicism's aversion to abortion is more absolute and the issues more clear-cut than with foreign or economic policies.

To a conservative like Deal Hudson, editor of Crisis magazine and a Bush campaign adviser, it would be "disastrous" if Kerry, "with such aggressive pro-abortion policies," becomes the world's most prominent Catholic politician."

"He thinks bishops should stress their nonpartisanship, but denounce Kerry's abortion dissent in letters read from every pulpit in the land.

With few exceptions, he complains, "pro-abortion Democrats have had a free ride from the hierarchy for 30 years."

Other militants want abortion-rights supporters barred from campaigning at Catholic institutions. In 2000, Bishop James Timlin of Scranton, Pa., disinvited Al Gore from a hospital and thereafter the candidate was barely seen in Catholic venues.

But the Rev. Reese says that's difficult with Catholic colleges, which are mostly controlled by religious orders, not bishops, and favor open forums. The Rev. Reese says the strongest protests erupt when Catholic campuses give honorary degrees to Catholics who support abortion rights.

A special panel of the U.S. hierarchy, led by Cardinal Theodore McCarrick — who isn't comfortable denying Communion — is sorting through what sanctions to impose on politicians. But it's not clear that action will come before Election Day.