"We hope that everyone would treat [each other] that way no matter which side of this issue they were on," said Elder L. Whitney Clayton, of The Church of Jesus Christ of Latter-day Saints' Presidency of the Seventy.
Proposition 8 amends California's constitution to define marriage as legal only between one man and one woman. It overturns a June ruling by the California Supreme Court striking a 2000 ban on such unions. Since then, some 18,000 gay and lesbian couples were married in California - among them couples from Utah.
Kate Kendell, director of the National Center for Lesbian Rights in San Francisco, said the center and the California attorney general believe those marriages will remain valid.
By Wednesday, three lawsuits asked the California Supreme Court to overturn the proposition, and two of them asked the court to block it from taking effect while legal cases are pending.
The lawsuits were filed by the American Civil Liberties Union, Lambda Legal and the National Center for Lesbian Rights.
Unofficial returns show the measure passing with a 440,000 vote margin. But 3 million ballots remain uncounted, which Kendell said made the outcome too close to call.
"It's a very steep climb back," she said. "If tomorrow indicates that those ballots are from counties which voted overwhelmingly to defeat Prop 8, then we will have to look seriously at a possibility of making that climb."
The LDS Church's campaign to pass Proposition 8 was its most vigorous since the 1970s, when it helped defeat the Equal Rights Amendment.
Asked whether the LDS Church would engage in similar activism in the future, Clayton said, "It depends on the issue, and the time and what is going on."
In a statement, the LDS Church said it does not object to domestic partnership or civil union legislation "as long as these do not infringe on the integrity of the traditional family or the constitutional rights of churches."
As for Proposition 8, "we consider this to be a moral issue," Clayton said. "We're not anti-gay, we're pro marriage between a man and a woman."
But the outcome dismayed gay couples like Russ and Joe Baker-Gorringe, of Salt Lake City, who married religiously in Utah in 2007 and then were legally married in California in October.
"We would be the first to defend the LDS Church's right not to perform or recognize our marriage," Russ Baker-Gorringe said. "But it is morally wrong for any church to deny my church, which does believe in marriage equality, the right to marry who we love."
An estimated $70 million was spent for and against the measure. Clayton said the LDS Church was "most grateful" for the "generous sum" contributed by its members. The church itself gave only indirect support - paying, for instance, for his hotel during trips to California.
Kendell said LDS Church members' time and money were key to the effort against the proposition, and she respects that.
"What I find very painful and in some respects unforgivable is that the church would ally itself with the outright falsehoods and distortions of the Prop 8 campaign," she said.
And the campaign proved divisive for many LDS Church members, some of whom were chastised by church leaders and other members for their opposition. Some said the church's activism led them to a personal crisis of faith.
Clayton said he had no firsthand knowledge of such hostility, and advised members hurt or confused by the church's involvement to seek counsel with their bishop to understand the doctrinal basis for the church's position.
He also said any action regarding members who spoke out against the measure would be left to local church leaders' discretion.
Morris Thurston, of Orange County, an LDS member who opposed the ballot initiative, said he received a lot of "feedback that was either outright hostile or self-righteous preaching" from strangers because of his moral concern about imposing religious beliefs on others.
Thurston's hope is that Latter-day Saints on both sides of the issue "will reach out and try to embrace people who might not have agreed with them. It doesn't mean we will change our minds about it, but it does mean we need to be brothers and sisters in the gospel."
* THE ASSOCIATED PRESS contributed to this report.