DENVER -- Colorado voters on Tuesday approved an amendment to the state constitution to define marriage as a relationship between one man and one woman and at the same time, rejected a proposal that would have given same-sex partners the same rights as married couples.

With 88 percent of the expected vote counted, 56 percent of Colorado voters had backed Amendment 43, defining marriage as a union between one man and one woman. Referendum I was rejected, 53 percent to 47 percent.

Colorado joined more than two dozen other states in amending their constitutions to declare marriage must be a union between a man and a woman. Referendum I supporters had been hoping returns from Denver, where voting was slowed because of computer problems and new voting machines, would help them pull out a win.

Instead, gay rights supporters had a double-barreled loss.

Business owner John Lindsey, 48, of Glenwood Springs voted for Amendment 43 and against Referendum I.

"I'm not anti-gay, so to speak, but there are a lot of ramifications that go around that," said Lindsey, a married Republican who described himself as a traditionalist.

Dawn Pope, 41, a married mother of two in Lakewood who described herself as a conservative Christian and unaffiliated voter, said she voted against both measures.

"I do believe that marriage is between a man and a woman," she said. "I have friends that are gay, and I know that they receive the same medical rights that I do. So there isn't a need for another amendment to put out there to give them anything additional because they are receiving it in the state of Colorado. And they told me that."

Among other things, Referendum I would allow the couples to adopt children and require alimony and child support if they separate. It would also ensure that their partners can make medical decisions for them and the right to inherit property even without a will.

Supporters of Amendment 43 had hoped a recent court decision in New Jersey ordering lawmakers to endorse gay marriage or civil unions would boost turnout here. Yet Colorado was rocked last week by the resignation of evangelical leader Ted Haggard -- a prominent backer of the amendment -- amid allegations that he paid for gay sex.

Denver pollster Floyd Ciruli said the allegations against Haggard likely helped sway undecided voters against Referendum I.

"The goal of the gay-rights advocates was to keep it very low key," Ciruli said, but instead Haggard's troubles put a spotlight on the issue.

"What they had was a huge controversy on the front page related to the most controversial aspects of the gay lifestyle," Ciruli said.

"The courts are willing to take a lead on this and decide the definition of marriage if Colorado voters don't," said Jon Paul, spokesman for the pro-43 group Coloradans for Marriage. He declined comment on whether Haggard's dismissal affected last-minute campaigning.

Carrie Gordon Earll, director of issues analysis for Focus on the Family's public policy arm, said most voters had made up their minds before the Haggard scandal broke last week.

She said Colorado voters saw Referendum I as marriage by another name.

"Referendum I was sold to the public as hospital visits, and clearly it was much more than that. It was the legal equivalent of marriage," she said.

Referendum I says domestic partnerships are not marriages, though opponents said it delivered the same benefits enjoyed by spouses.

Joshua Tafoya, 22, a literature major at Mesa State College in Grand Junction, voted against the marriage amendment and yes on Referendum I. He said whatever goes on in someone's bedroom isn't his business or the government's.

"Personally if it were me, and I was on my deathbed, I would want to give what I want to who I want without the state intervening," said Tafoya, a single Democrat.

Even though there were plenty of high-profile issues on the 14-item state ballot, it was the gay marriage debate that drew the most attention and money. Colorado-based software millionaire Tim Gill contributed some $3 million in backing Referendum I and fighting Amendment 43.

On the other side was Focus on the Family, the Colorado Springs-based evangelical Christian organization, contributing at least $874,000 through its public policy arm.

State law already defines marriage as being between one man and one woman, but Amendment 43 supporters said that could be overturned by a judge and the better move was a constitutional amendment.

Both sides said the two competing measures presented an unusual situation.

"It does provide the voters with the opportunity to cast a more nuanced vote for what they really want," said Bob Loevy, a political science professor at Colorado College.

The domestic partnership campaign began running television ads early that emphasized the problems faced by same-sex couples under current law.

In one, a man waited anxiously in a hospital waiting room. Supporters stressed the proposal wasn't the same as marriage, contrasting a happy bride and groom outside church with gay couples showing up in a drab government office for a domestic partnership certificate.

Among other things, Referendum I would have allowed gay couples to adopt children and require alimony and child support if they separate. It would have ensured their partners can make medical decisions for them and the right to inherit property even without a will.

Denver massage therapist Carissa Macklin, who is gay, voted for Referendum I and against Amendment 43. She said she doesn't care so much how gay partnerships are labeled but whether they'll have the right to share custody of their children or inherit property.

"I just believe we should have the same rights as everyone else. What it's called isn't important to me," said Macklin, who is unaffiliated with any major party.

Harold Davenport, 70, a math professor at Mesa State College in Grand Junction, voted for Amendment 43 and against Referendum I because he said sex should only be for reproduction.

"Those people are sick," he said of gays.