DENVER, May 6 — Colorado is set to become a bruising and confusing battleground over marriage and same-sex unions this year, with up to four conflicting proposals competing for a spot on the November ballot.

So far, the only proposal with a guaranteed place on the ballot — approved on Thursday by the state House of Representatives and sent directly to the voters — is the Domestic Partnership Benefits and Responsibilities Act, known as 1344 for its bill number in the Legislature.

It would give same-sex partners many rights of married couples, including the ability to adopt each other’s children and to make medical decisions on the other’s behalf.

After that things become more complicated.

Opponents of 1344 have mounted an effort to get enough voter signatures for a proposed amendment to the state Constitution that would short-circuit the Partnership Act, by barring legal recognition of any status “similar to marriage.”

A third proposal would attack 1344’s attackers. The sponsors of that proposal want to enshrine in the Constitution a statement intended to protect the Partnership Act by declaring that such unions are not “similar to marriage.” A fourth ballot proposal would strengthen the law banning same-sex marriage by putting that ban into the Constitution.

“Clear as mud, right?” said Sean Duffy, a spokesman for Coloradans for Fairness and Equality, which supports 1344.

At least six other states — Idaho, South Carolina, South Dakota, Tennessee, Virginia and Wisconsin — are offering similar proposals.

Colorado’s discussion is messier because it has one of the lowest thresholds for direct citizen participation. Signatures of only 5 percent of the people who cast votes for the secretary of the state in the last election are required to get a constitutional proposal on the ballot — about 68,000 people this year.

Most of the 17 other states that allow direct petition for constitutional amendments require signatures of 8 percent to 15 percent of voters in a past election.

People involved in the petition process said that competing efforts would surely make for a tougher fight through the summer and fall.

Television advertising has already begun for 1344, including a spot showing a distraught-looking man pacing a hospital corridor, frozen out of making medical decisions for his male partner, the announcer says, because Colorado does not recognize their relationship.

Opponents of 1344 say it basically creates gay marriage while avoiding the phrase.

People on both sides say that no matter what voters do a court fight is likely, if only to define “similar.”

Kevin Lundberg, a Republican legislator who is fighting the Partnership Act with his proposal to ban “similar” conditions to marriage, said his effort would give voters “a very thorough range” to weigh in on.

Mr. Lundberg opposed 1344 in the Legislature, but conceded that having it on the ballot would help in gathering signatures for his effort. The deadline for petitions is Aug. 7.

A spokesman for Coloradans for Marriage, which is backing a constitutional amendment defining marriage as between a man and a woman — with support of conservative groups like Focus on the Family, based in Colorado Springs — said that 1344 would probably galvanize conservative voters in some places.

“Some segments just want the marriage amendment passed and don’t care about the domestic partnership stuff,” said Jon Paul, the group’s executive director.