The "Commitment Campaign," led by the centrist Democrat group Third Way, was to be launched Monday, USA Today reported.
The campaign has received backing from Maryland Gov. Martin O'Malley, a Democrat; Rhode Island Gov. Lincoln Chafee, an independent; former New Jersey Gov. Christine Todd Whitman, a Republican; and Ken Mehlman, former chairman of the Republican National Committee.
Same-sex marriage supporters have argued the unions should be legalized to give gays and lesbians equality.
But a poll by Third Way and Grove Insight suggests that approach could lead Americans in the middle on the gay marriage debate to believe gays and lesbians want to marry for different reasons than straight couples.
In the poll, when asked why "couples like you" might want to marry, 58 percent of respondents said to "publicly acknowledge their love and commitment to each other." But asked why gays and lesbians may want to marry, respondents split between "love and commitment" and "rights and benefits."
"In this fast-evolving issue, we're all searching for common ground," O'Malley told USA Today. "And the way to have a conversation with those who would be inclined not to support marriage equality is to search for those common values that we share."
The campaign opens as the Senate Judiciary Committee is set this week to repeal the Defense of Marriage Act, which defines marriage as a legal union between a man and a woman and prevents the federal government from recognizing same-sex unions as valid marriages.
Several states, including Maryland, Minnesota and North Carolina, are likely to consider gay marriage legislation or ballot initiatives in 2012, USA Today said.