ROME, June 30 — Scientists who engage in stem cell research using human embryos should be subject to excommunication from the Roman Catholic Church, according to a senior Vatican official.

Cardinal Alfonso López Trujillo, who heads the group that proposes family-related policy for the church, said in an interview with the Catholic weekly Famiglia Cristiana published Thursday that stem cell researchers should be punished in the same way as women who have abortions and doctors who perform them.

"Destroying an embryo is equivalent to abortion," said the cardinal. "Excommunication is valid for the women, the doctors and researchers who destroy embryos."

It was unclear if the pope supported the position, and the Vatican did not return calls for comment. But such blunt remarks from a powerful cardinal just a week before the church convenes a meeting to discuss the topic could foreshadow a hardening of Vatican policy on the issue, experts said.

On Saturday, Cardinal Trujillo will open the church's fifth World Meeting of Families in Valencia, Spain, and Pope Benedict XVI will attend on July 9, the closing day. As head of the Pontifical Council for the Family, it will be up to Cardinal Trujillo to propose new church policies, though adopting any such measure could require a long and complicated process.

The church has long opposed embryonic stem cell research, and has campaigned against any medical procedure or research technique that harms human embryos or fetuses.

But the threat of individual excommunication — the most serious punishment meted out by the church — was previously directed at women and medical personnel who participated in abortions. Cardinal Trujillo's stand would broaden the use of that sanction to biomedical researchers who use embryos.

"The cardinal's view is that the penalty of excommunication should be extended to stem cell research," said the Rev. Brian Johnstone, a moral theologian at the Alphonsian Academy here. "The provisions of canon law about what leads to excommunication are very precise."

But Father Johnstone cautioned that it was unlikely that the church would formally adopt a final position next week. "Clarification of such a delicate point of this importance is unlikely to be made at such a large gathering," he said.

Even some Catholics who are opposed to the use of embryos in research felt that excommunication was too strong a sanction. "If we're defending the principle that human life should not be touched, it should not be done in a punitive, castigatory or burn-in-hell sort of way," said Paola Binetti, a leading Catholic politician here.

The specification of the punishment for embryonic stem cell research was partly needed so the church could catch up with advances in science.

When the 1990 Evangelium Vitae came out reaffirming that abortion would lead to automatic excommunication, "Embryonic stem cell research was not a front-page issue," Ms. Binetti said.

While doctors and scientists claim that embryonic stem cell research holds the promise to cure many intractable diseases, the church opposes the practice because human embryos are used to harvest cells for the work. Some of these embryos are left over after in vitro fertilization procedures, but scientists can also create embryos themselves.

The church regards such early-stage embryos as a human life, not to be used or destroyed. It maintains that there are other ways to obtain stem cells for research purposes — from umbilical cord blood after a birth, for example — though it acknowledges that they are significantly more cumbersome.

According to current church law, excommunication for abortion is "latae senentiae," meaning that it is automatic and does not require an action or proclamation by a church official. This type of excommunication is reserved for acts deemed so serious that no verdict or judgment is required. Even so, many women who have had abortions continue to practice Catholicism, and many parishes take pains to embrace and reintegrate them into church life.

Other acts that result in automatic excommunication include violence against the pope and consecrating a bishop without authorization. Now, experts said, Cardinal Trujillo's remarks raise the possibility that being involved in stem cell research might be added to the category. Secret Papal Archives to Be Opened

ROME, June 29 — The Vatican has authorized secret files from Pope Pius XI and his pre-World War II pontificate, from 1922 to 1939, to be released from their secret archives.

In 2003, under Pope John Paul II, the Vatican released archival material from the same period in an effort to allay accusations that the Vatican did not do enough to save Jews from the Holocaust.

For years, the Vatican has struggled to defend the reputation of Pius's successor, Pope Pius XII, who has been accused of shirking his responsibilities by looking the other way during the atrocities of World War II.

Peter Kiefer contributed reporting from Rome for this article, and Elisabetta Povoledo from Milan.

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