Meeting the bishops of Minnesota, North Dakota and South Dakota, who were making their "ad limina" visits to report on the status of their dioceses, the Pope said ignorance of or challenges to church teaching on marriage and sexuality were part of the "intellectual and ethical challenges" to evangelization in the United States today.

The Pope did not focus on current tensions between the U.S. bishops and the Obama administration, particularly over health care coverage of contraception and other practices that violate church teaching. But at the beginning of his speech, Pope Benedict reiterated his concern about "threats to freedom of conscience, religion and worship which need to be addressed urgently so that all men and women of faith, and the institutions they inspire, can act in accordance with their deepest moral convictions."

Concentrating his remarks on the need to promote and explain church teaching on sexuality, the Pope said the church's key concern is "the good of children, who have a fundamental right to grow up with a healthy understanding of sexuality and its proper place in human relationships."

Acknowledging the clerical sexual abuse scandal, the Pope said, "It is my hope that the church in the United States, however chastened by the events of the past decade, will persevere in its historic mission of educating the young and thus contribute to the consolidation of that sound family life, which is the surest guarantee of intergenerational solidarity and the health of society as a whole."

The moral virtues espoused in the church's teaching on sexuality are "the key to human fulfillment," he said, because they promote sexuality as "a source of genuine freedom, happiness and the fulfillment of our fundamental and innate human vocation to love."

"The richness of this vision is more sound and appealing than the permissive ideologies exalted in some quarters," which are "powerful and destructive," he said.

One of the first steps, he said, must be to help Catholics "recover an appreciation of the virtue of chastity," which forms the human heart to love in the most authentic way.

Pope Benedict told the bishops he was aware of "the powerful political and cultural currents seeking to alter the legal definition of marriage" so that it would include same-sex couples.

"The church's conscientious effort to resist this pressure calls for a reasoned defense of marriage as a natural institution," which is "rooted in the complementarity of the sexes and oriented to procreation," he said.

"Sexual differences cannot be dismissed as irrelevant to the definition of marriage," the Pope said.

Defending traditional marriage is not simply a matter of church teaching, he said; it is a matter of "justice, since it entails safeguarding the good of the entire human community and the rights of parents and children alike."

Pope Benedict praised the U.S. bishops' 2009 letter, "Marriage: Love and Life in the Divine Plan," and he asked them to continue reviewing and strengthening both religious education materials and marriage preparation programs.

In conversations with the bishops during the "ad limina" visits, he said, some of the bishops have expressed concern about how difficult it is to communicate the church's teaching effectively and some have told the Pope there are decreasing numbers of young people in their dioceses asking to be married in the church.

"We cannot overlook the serious pastoral problem presented by the widespread practice of cohabitation, often by couples who seem unaware that it is gravely sinful, not to mention damaging to the stability of society," Pope Benedict said.

The Pope said that in responding to situations in which many engaged couples already are living together, there must be "clear pastoral and liturgical norms for the worthy celebration of matrimony which embody an unambiguous witness to the objective demands of Christian morality, while showing sensitivity and concern for young couples."

Pope Benedict did not suggest specific norms or provide guidance on how insistent priests should be that cohabitating couples live separately before a church wedding.

The church itself "must acknowledge deficiencies in the catechesis of recent decades, which failed at times to communicate the rich heritage of Catholic teaching on marriage as a natural institution elevated by Christ to the dignity of a sacrament, the vocation of Christian spouses in society and in the church, and the practice of marital chastity," he said.

The speech was the Pope's third address to groups of U.S. bishops making their "ad limina" visits in 2011-2012. Because the Pope is not delivering a formal talk to each of the 15 groups of visiting U.S. bishops, the Vatican said the March 9 speech also was addressed to bishops from Indiana, Illinois, Wisconsin, Iowa, Missouri, Nebraska and Kansas.

Archbishop John C. Nienstedt of St. Paul and Minneapolis, speaking on behalf of the bishops, thanked Pope Benedict for announcing a special Year of Faith, which will begin in October.

"There is a profound crisis of faith affecting large numbers of people in today's society," the archbishop said. "Secular values have taken hold in many minds and hearts, causing a rejection of the very notion that true human happiness is found in conforming our lives to the will of God."

He thanked Pope Benedict for "the extraordinary leadership that you are providing in these turbulent times."