Archbishop Raymond Burke, who leads the Vatican supreme court, said President Barack Obama "could be an agent of death" if his support for abortion rights becomes a model for leaders in other countries.
Burke also said parishioners should press US bishops to withhold Holy Communion from Roman Catholic politicians who back legalized abortion. The archbishop made the comments to anti-abortion activist Randall Terry in a videotaped interview that Terry showed on Wednesday in Washington.
"It is weakening the faith of everyone," Burke said. "It's giving the impression that it must be morally correct to support procured abortion."
Terry conducted the interview as part of his campaign to persuade the church to oust American bishops who allow abortion rights backers to receive Communion. He said in a phone interview that Burke knew the goal of the campaign and that the interview would be distributed.
Burke, the former St Louis prelate, could not be reached on Wednesday through his Vatican office.
Michael Sean Winters, a Catholic journalist and blogger for the Jesuit magazine America, said Burke's linking himself in any way with Terry's effort violated Vatican protocol.
"It is unheard of for bishops not to defend each other in the face of zealots who are calling for their removal," Winters said. James Hitchcock, a St Louis University historian who was friendly with Burke when he led the local archdiocese, called the archbishop's comments "highly unusual."
Each bishop has the authority to decide how to present church teaching in his diocese. Bishops answer only to the pope. During the 2004 election, when Burke was still in St Louis, he sparked a rare public disagreement among US bishops over the issue. He said he would deny Communion to Massachusetts Sen John Kerry, the Democratic presidential nominee and an abortion rights supporter.
A small minority of US bishops took the same stand. Most American prelates say they privately discuss the issue with Catholic lawmakers and lobby all members of Congress and the president against the procedure.
The White House press office did not respond to a request for comment. Obama has pledged to find ways to reduce the abortion rate, to find common ground with opponents.