SAO PAULO, Brazil — Pope Benedict XVI addressed sexual morality in a speech to tens of thousands of young Catholics, instructing young people to avoid premarital sex, remain faithful once they are married and to promote life from "its beginning to natural end."

The latter was an oblique reference to abortion, the issue that has dominated Benedict's first visit to Latin America since he succeeded John Paul II two years ago.

Earlier Thursday, the Vatican released a transcript that seemed to backtrack on the pope's remarks during his flight from Rome, when he suggested that Catholic lawmakers who vote to legalize abortion should excommunicate themselves.

The Roman Catholic Church prohibits abortion, which is illegal in Brazil as in most of Latin America except in cases of rape or where the woman's life is in danger. Yet while church law says anyone who procures an abortion is automatically excommunicated, the Vatican's policy on politicians who favor abortion rights is the subject of a growing debate.

The pope's speech at a Thursday evening youth rally at a soccer stadium in São Paulo was sure to resonate across the region, home to more than half the world's 1.1 billion Roman Catholics.

Delivered in Portuguese, Benedict's address was lengthy and full of moral instruction, notably concerning sexual conduct. Saying young people were the future of the church, the 80-year-old pope warned against drug use, violence, corruption and the temptations of wealth and power.

"Seek to resist forcefully the snares of evil that are found in many contexts," he told the crowd of some 40,000, with thousands more camped outside the stadium.

He made no mention of the church's battle against Brazil's free distribution of condoms to combat AIDS, but implored his young audience to promote life from "its beginning to natural end." The Vatican prohibits contraception, in addition to abortion, euthanasia and in vitro fertilization.

Benedict called for fidelity between spouses and chastity "both within and outside marriage" — church language for responsible sex — and instructed the young to build a society based on Christian moral values.

The crowd burst into a loud cheer when he mentioned his predecessor, the late John Paul, who visited Brazil three times. But they also shouted, "I love you," when Benedict finished talking.

Many in the crowd shared the pope's views — polls show that Brazilians are overwhelmingly against expanding access to abortion. But beyond the stadium, the pope's comments on excommunicating politicians who favor legalizing abortion continued to provoke debate.

Catholics have been arguing whether politicians who approve abortion legislation, as well as doctors and nurses who take part in the procedure, subject themselves to automatic excommunication under church doctrine.

Asked during an in-flight news conference Wednesday whether legislators who legalized abortion in Mexico City should rightfully be considered excommunicated, Benedict answered "Yes."

But his spokesman, the Rev. Federico Lombardi, later said Benedict did not intend to formally excommunicate anyone — a rare process under church law — and on Thursday the Vatican released a slightly edited transcript that dropped the word "yes" from the pope's response.