Topeka ? Voters will decide in less than nine weeks whether Kansas will join 17 other states in adding a ban on same-sex marriage to the state constitution, as well as denying civil unions and possibly other benefits to gay couples.

The proposed constitutional amendment, on the ballot statewide on April 5, would declare that only married couples of one man and one woman would be entitled to the benefits associated with marriage.

Supporters, who are confident voters will approve, say the amendment merely would preserve existing state policy.

Some opponents, pessimistic about their chances of defeating the amendment, argue it could hurt unmarried heterosexual couples or prevent private companies from offering benefits to gay employees’ partners.

The measure cleared the Kansas House on Wednesday to go on the ballot. The Senate adopted the measure last month, and the House vote was 86-37, three more than the two-thirds majority necessary.

Changing the constitution will require approval by a simple majority of voters, but some supporters expect the margin to be overwhelming. The Rev. Jerry Johnston, senior pastor at Overland Park’s First Family Church, predicted at least 80 percent of voters would approve the amendment.

“The state of Kansas is going to reflect the nation,” Johnston said after the House vote. “The minority voice has been silenced by the majority, and you’re going to see it on April 5.”

In Lawrence, Stephanie Bryson, a 37-year-old University of Kansas researcher, said she worries the amendment would nullify her decision to grant her female partner power of attorney to make health care decisions for her. Bryson was diagnosed with thyroid cancer two years ago.

“It does definitely send a message that we’re not valued,” she said. “It stirs up a lot of fear for a lot of us.”

In Kansas, the House rejected a similar proposal last year, surprising and angering clergy and other supporters.

Those supporters argued amending the constitution would protect the state’s traditional definition of marriage from legal challenges.

And Kent Hampton, of Manhattan, a 49-year-old research assistant at Kansas State University who supports the amendment, said action by states may push Congress to adopt a marriage amendment to the federal Constitution.

“It’s really important to keep the momentum going,” he said.

Some supporters worried about what they see as a growing tolerance for homosexuality, which they view as harmful. They also said the state should declare its support for traditional families.

“It’s the basic building block of our society, and if we can’t protect that, our whole society will crumble,” said the Rev. Paul Barkey, a retired Army chaplain and pastor of the Ashland Community Church outside Manhattan.

Some critics, including Gov. Kathleen Sebelius, questioned whether amending the constitution is necessary. Kansas law has recognized only marriages between one man and one woman since 1867.

Other opponents called the amendment discriminatory and suggested many legislators didn’t know — or perhaps didn’t care — that it could have broad ramifications for both gay and unmarried heterosexual couples. Supporters said their fears are unfounded.

A similar debate arose in Utah, which adopted an amendment last year. However, the Utah Senate on Tuesday rejected a domestic partner registry to protect the rights of unmarried gay and heterosexual couples, with lawmakers saying it wasn’t necessary.

Meanwhile, the Idaho Senate on Wednesday rejected a proposal to add a gay marriage ban to that state’s constitution, for the second consecutive year.

In Kansas, opponents of an amendment thought their best chance of defeating the measure lay with legislators, not in a statewide campaign.

“It’s going to be impossible for us,” said Tiffany Muller, a Topeka City Council member and lobbyist for the Kansans for Equal Justice Project. “We’re going to have to run on a shoestring budget and rely on a lot of volunteers.”

Thirteen of the 17 states with constitutional gay marriage bans enacted them last year, with majorities ranging from 57 percent in Oregon to 86 percent in Mississippi. In Missouri, an amendment received 71 percent approval.

“It may be a point of losing by less than a 70-30 split,” said Steve Brown, of Prairie Village, the president of the state Democratic Party’s Lesbian, Gay, Bisexual and Transgendered Caucus.

In other legislative action, gambling lobbyists trotted out a new proposal for state-owned casinos, arguing it would provide new money for education while tapping into a lucrative tourism industry.

Also, the Senate approved a bill designed to increase disclosure of campaign contributions in the days leading up to an election.