DENVER — A proposal to grant gay couples rights similar to marriage is expected to pass its first vote from Colorado lawmakers.

A Senate committee is hearing testimony Wednesday from gay couples and supporters of traditional marriage on a civil unions bill that is expected to become law this year. Democrats tried unsuccessfully the past two years to pass civil unions, but House Republicans have defeated the measure. But Democrats now control both chambers of the legislature and Democratic Gov. John Hickenlooper supports the measure.

Democratic Sen. Pat Steadman, the bill sponsor, said he would prefer to have marriage for gay couples but the state constitution doesn’t allow it.

“We have a constitutional prohibition in Colorado against marriage equality and as a legislator I can’t change the constitution. I can change the state laws, and that’s what I’m setting out to do — to do the next best thing, something that is admittedly lesser, and separate and unequal, but still something to provide very meaningful protections to families all across the state.”

Republican Sen. Steve King opposes the bill and will be voting against it in committee Wednesday.

He said he knows gay rights groups may push for same-sex marriage later, depending on what the U.S. Supreme Court rules when it considers arguments in the coming months on California’s gay marriage ban.

“I will continue to push back against those powers that want gay marriage in Colorado.”

Brad Clark, the executive director of One Colorado, which has been pushing for civil unions, said the issue is no longer controversial for many people.

“I think what we’re seeing is that people’s hearts and minds are really changing.”