SALT LAKE CITY - Mormon leaders vowed to be a leading advocate for the belief that marriage is an institution exclusive to a man and a woman during their biannual conference Saturday that also included two rare events.

The first was when the conference kicked off without the usual welcoming address from church president Thomas S. Monson, 87, who days earlier also missed a meeting with President Obama.

Monson had decided to reduce the number of speeches he's giving this weekend, church officials said.

The second unusual event was when five people stood and yelled, "Opposed," during a part of the conference when attendees usually raise their hands in unison in a vote of support for church leadership. They drew some gasps from surprised attendees and represented only a handful of the 20,000 in attendance.

L. Tom Perry, a member of the faith's Quorum of the Twelve, cautioned Mormons not to be swayed by a world filled with media and entertainment that presents the minority masquerading as the majority and tries to make mainstream values seem obsolete.

He said strong, traditional families are the basic units of a stable society, a stable economy, and a stable culture of values.

"We want our voice to be heard against all of the counterfeit and alternative lifestyles that try to replace the family organization that God himself established," Perry said.

As acceptance of gay marriage has swelled in recent years and same-sex unions have become legal in dozens of states, including Utah, the church's stance on homosexuality has softened.

Church leaders helped push through a Utah law this year that bars housing and employment discrimination against gay and transgender individuals while also expanding protections for the rights of religious groups and individuals.

But the church has taken time during several recent conferences to emphasize its insistence that marriage should be limited to unions between a man and a woman. In April 2014, Neil L. Andersen of the quorum said, "While many governments and well-meaning individuals have redefined marriage, the Lord has not."