It seems a can’t-lose proposition: Ask voters to ban same-sex marriages, and they consistently endorse the idea, from the South to the West.

Kansas on Tuesday became the latest and 18th state to pass a constitutional amendment barring gay marriage. With conservatives pushing to define marriage as between a man and woman throughout the country, similar proposals are on the ballot in three other states next year and more than a dozen are considering them.

New England has been the major holdout; there, legislators and judges have strengthened rights for gays and lesbians. The Connecticut Senate on Wednesday voted to legalize civil unions. If the bill becomes law, Connecticut would be the only state to do so without a court order demanding lawmakers act.

Kansas voted by a more than 2-to-1 margin Tuesday to ban gay marriages and civil unions, and voters also ousted the lone gay city council member in Topeka, Tiffany Muller, who had defeated an emphatically anti-gay opponent in the primary.

The New England examples — most decisively Vermont’s civil unions and Massachusetts’ legalized gay marriages — are seen by ban supporters as the threat that’s helping their cause. Advocates for gay marriage also see those examples as a plus, by proving that fears gay marriage will somehow destroy society’s social fabric are unfounded.

“The more places that we are able to extend the same rights and responsibilities to all Americans, the more places we’ve got a light to shine on what’s happening,” said Joe Solmonese, president of Human Rights Campaign, a gay-rights lobbying group.

New England states aren’t the only ones to offer gay-rights advocates hope. California, Hawaii and New Jersey also allow for domestic partnerships, though California and Hawaii also have states laws that define marriage as between a man and a woman.

Connecticut offers the strongest recent pro-gay legislation, by extending all rights and privileges of marriage to same-sex couples but without an actual marriage license.

On Wednesday, the state Senate voted 27-9 to recognize civil unions; proponents say the bill will likely clear the House, also controlled by the Democrats, possibly as early as next week. Republican Gov. M. Jodi Rell has said she supports the concept of civil unions.

For ban supporters, the key difference is a vote of the people.

“When the people are given a chance to decide, their view is overwhelming,” said Peter Sprigg at the conservative Family Research Council. “Every state that had this on the ballot passed it. It shows to me there is a tremendous grass-roots consensus that marriage is between a man and a woman.”

Voters will decide the question in Alabama in June 2006, and in South Dakota and Tennessee at the November 2006 election.