LOS ANGELES (CBS) — Mayor Antonio Villaraigosa announced plans Friday to co-chair a new initiative aimed at passing a national gay-marriage law backed by 80 mayors nationwide.

Villaraigosa will lead “Mayors for the Freedom to Marry” with New York City Mayor Michael Bloomberg and San Diego Mayor Jerry Sanders.

“If we truly believe in family values, we should value all families,” Villaraigosa said. “Denying gay and lesbian couples the freedom to marry weakens society by hurting our communities, neighbors and families.”

The mayor’s group is an off-shoot of “Freedom to Marry,” a national organization that partners with local groups to push for same-sex marriage. The mayors will urge their cities to pass laws allowing gay marriage. They will also encourage their congressional delegations to repeal the Defense of Marriage Act, which defines marriage as between a man and a woman.

Marc Solomon, national campaign manager of Freedom To Marry, said national polls now show a majority of Americans support gay marriage.

“Many Americans who for decades opposed the freedom to marry for same-sex couples are rethinking their position, and hearts and minds are changing,” Solomon said.

Sanders, a Republican who co-chairs the campaign, said his views on gay marriage had evolved.

“Marriage encourages people to take responsibility for each other, provides greater security for children, and helps our country live up to the promises set forth in our founding documents,” Sanders said.

(©2012 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services contributed to this report.)