Cardinal O’Brien, whose office had initially said he would fly to Rome before the conclave, has been the head of the Catholic Church in Scotland since 1985 and was named a cardinal by Pope John Paul II in 2003. He was among the cardinals who attended the conclave that chose Benedict as John Paul’s successor in 2005.

The main role of cardinals is to elect a new pope, and they remain eligible to vote under any circumstances, even if they have been excommunicated, Bishop Juan Ignacio Arrieta, the secretary for the Pontifical Council for Legislative Texts, said last week.

Ambrogio Piazzoni, a papal historian, told reporters last week that he could think of no examples of cardinals who had refrained from voting for anything other than health reasons, or from the pressures of different governments in past years.

Terence McKiernan, the president of BishopAccountability.org, a nonprofit Web site based in Massachusetts that seeks to collate documentation about the sexual abuse crisis, said the move set a new precedent.

“Many cardinals scheduled to join the conclave have been involved as bishops in handling cases of clergy sexual abuse, and some of them have done such a bad job that they, too, should recuse themselves from the conclave,” he said in an e-mailed statement, naming Cardinal Mahony and the leaders of the church in two scandal-scarred countries, Cardinal Sean Brady of Ireland and Cardinal Godfried Danneels of Belgium. “If they are involved in the deliberations and the votes, they will taint the outcome, damaging the legitimacy of whoever is ultimately chosen.”

The resignation was met with mixed responses in Scotland, ranging from satisfaction among gay and lesbian groups to dismay among others who saw Cardinal O’Brien as a strong voice for Scotland and its 750,000 Catholics, as well as an influential advocate for the poor and aid to the developing world. He has been a frequent visitor to Catholic missions in Africa.

Among some, there was upset that the cardinal had been brought down by accusers who have so far not identified themselves publicly, and whose allegations have yet to be tested by any ecclesiastical tribunal, or by a Scottish court. There was strong endorsement for the pope’s decision to accelerate the cardinal’s resignation and a hope that the episode would lead to a determination under a new pope to deal decisively with the legacy of sexual abuse among priests.