VATICAN CITY — Pope Benedict XVI’s surprise announcement on Monday that he will resign on Feb. 28 sets the stage for a succession battle that is likely to determine the future course of a church troubled by scandal and declining faith in its traditional strongholds around the world.

Citing advanced years and infirmity, Benedict became the first pope in six centuries to resign. Vatican officials said they hoped to have a new pope in place by Easter, while expressing shock at a decision that some said had been made as long as a year ago.

Saying he had examined his conscience “before God,” Benedict said he felt that he was not up to the challenge of guiding the world’s one billion Catholics. That task will fall to his successor, who will have to contend not only with a Roman Catholic Church marred by the sexual abuse crisis, but also with an increasingly secular Europe and the spread of Protestant evangelical movements in the United States, Latin America and Africa.

The resignation sets up a struggle between the staunchest conservatives, in Benedict’s mold, who advocate a smaller church of more fervent believers, and those who believe that the church can broaden its appeal in small but significant ways, like allowing divorced Catholics who remarry without an annulment to receive communion or loosening restrictions on condom use in an effort to prevent AIDS. There are no plausible candidates who would move on issues like ending celibacy for priests, or the ordination of women.