Vatican City - Even at the Vatican, not all sacred beliefs are absolute: Thou shalt not kill, but war can be just. Now, behind the quiet walls, a clash is shaping up involving two poles of near certainty: the church's long-held ban on condoms and its advocacy of human life.
The issue is AIDS. Church officials recently confirmed that Pope Benedict XVI had requested a report on whether it might be acceptable for Catholics to use condoms in one narrow circumstance: to protect life inside a marriage when one partner is infected with H.I.V. or is sick with AIDS.
Whatever the pope decides, church officials and other experts broadly agree that it is remarkable that so delicate an issue is being taken up. But they also agree that such an inquiry is logical, and particularly significant from this pope, who was Pope John Paul II's strict enforcer of church doctrine.
"In some ways, maybe he has got the greatest capacity to do it because there is no doubt about his orthodoxy," said the Rev. Jon Fuller, a Jesuit physician who runs an AIDS clinic at the Boston Medical Center.
The issue has surfaced repeatedly as one of the most complicated and delicate facing the church. For years, some influential cardinals and theologians have argued for a change for couples affected by AIDS in the name of protecting life, while others have fiercely attacked the possibility as demoting the church's long advocacy of abstinence and marital fidelity to fight the disease.
The news broke just after Benedict celebrated his first anniversary as pope, a relatively quiet papal year. But he devoted his first encyclical to love, specifically between a man and a woman in marriage.
Indeed, with regard to condoms, the only change apparently being considered is in the specific case of married couples. But any change would be unpopular with conservative Catholics, some of whom have expressed disappointment that Benedict has displayed a softer face now as defender of the faith than he did when he was still Cardinal Joseph Ratzinger, the papal adviser.
"It's just hard to imagine that any pope — and this pope — would change the teaching," said Austin Ruse, president of the Culture of Life Foundation, a Catholic-oriented advocacy group in Washington that opposes abortion and contraception.
It is too soon to know where the pope is heading. Far less contentious issues can take years to inch through the Vatican's nexus of belief and bureaucracy, prayer and politics, and Cardinal Javier Lozano Barragán, the pope's top aide on health care issues, and other officials declined requests for interviews.
The news reports have been contradictory, except to confirm that the pope has asked for such a review.
Cardinal Lozano Barragán was quoted in a daily newspaper, La Repubblica, as saying Benedict made the request two months ago, as part of a broader examination of bioethical issues. "My department is carefully studying it, along with scientists and theologians entrusted with drawing up a document about the subject," he was quoted as saying.
He backtracked slightly a few days later: "We are in the first stage," the cardinal told the Zenit News Agency, which specializes in covering the Catholic Church. Would there be a document? "There might or might not be."
The debate has two levels: one on moral theology and church doctrine, the other on public relations and politics. Many factors are driving the debate: The church is experiencing its greatest growth in Africa, which has the most severe AIDS problem. Much health care in Africa is provided by Catholic charities, whose workers often speak of being torn between church doctrine and the need to prevent disease.
More broadly, critics of the current Vatican policy say it is hard for the church to remain consistent on so-called life issues, like its opposition to abortion, euthanasia and the death penalty, when condom use can help prevent the spread of AIDS.
But there is a deep vein of feeling against any change. Some oppose any perceived erosion of Humanae Vitae, the 1968 encyclical that banned artificial contraception, while other opponents say approving condoms for AIDS prevention might be interpreted as a wider acceptance of their use.
"That will be picked up as 'Church O.K.'s Condoms,' and that would seem to undermine the whole church teaching on sexuality and marriage," said the Rev. Brian V. Johnstone, a moral theologian at the Alphonsian Academy in Rome.
The debate was reopened, in public at least, in a long discussion in the newsweekly L'Espresso last month between Cardinal Carlo Maria Martini, the retired archbishop of Milan and an influential thinker in the church, and an Italian bioethicist, Ignazio Marino.
"Certainly the use of prophylactics can, in some situations, constitute a lesser evil," Cardinal Martini said. "There is, then, the particular situation of spouses, one of whom is affected by AIDS."
But he recognized arguments against any such official statement, saying, "The question is really if it is wise for religious authorities to propagandize in favor of this method of defense, almost implying that the other morally defensible means, including abstinence, should be put on a secondary plane."
The moral arguments stretch back nearly two millenniums, to the idea that the church has a responsibility, in difficult moral cases, to advocate the "lesser evil."
"It is not considering that using a condom is morally good or right," Father Johnstone said. "You are simply trying to persuade that person to do the lesser evil — but it is still considered evil."
There are other related arguments: One is "self defense," in which an uninfected partner could demand condom use to protect against infection. Another is that using a condom against AIDS could be considered medical intervention rather than contraception.
But the "lesser evil" argument is not universally accepted among Catholic thinkers, and the theology is complicated. Among many other issues, there is the user's intent: whether it is possible to use a condom without the intention of contraception.
"Putting on a condom is clearly something someone chooses," the Rev. Thomas Berg, an ethicist and executive director of the Westchester Institute, an institute for Catholic studies in New York, said by e-mail. "And to do so in sexual relations, even if one's purpose is not to contracept, but merely to stop the spread of disease, one would still be opting for something that drastically disorders those sexual relations. And this, the church has taught to be immoral."
Echoing other conservative voices, Father Berg said he believed that in the end, Benedict would make no changes but use the debate to "vigorously re-endorse ethically acceptable answers to the AIDS crisis, namely, the virtue of chastity and abstinence."
But others point to what they say is Benedict's capacity to surprise, using the shorthand of "Nixon in China" to make the case that a hard-liner could, without reversing church doctrine, more easily make such a change.
Making a change would address a relatively small part of the problem because transmission of AIDS usually involves unmarried people. But if Benedict did so, "it will have a huge influence," said Rebecca Schleifer, a researcher on AIDS issues for Human Rights Watch, though that influence may be exactly what many in the Vatican fear.
She and other experts said it could help break down resistance to condom use in places like the Philippines or parts of Africa, where Catholic officials or clerics have a large influence.
"The church taking a step forward in saying, 'They do work and we believe in them in this situation' is important to help protect the lives and health of millions of people around the world," Ms. Schleifer said.