New Jersey's well-organized gay-rights advocates are finding that their adversaries, too, are getting ready for a legislative debate over same-sex marriage.

The National Organization for Marriage, established this year in Princeton, made itself known over the last few weeks with radio advertisements urging people to tell their lawmakers that allowing gay couples to marry would undermine the institution.

The group set up in New Jersey because it is one of the few states where there's a realistic chance that lawmakers will vote to allow same-sex marriage in the next few years.

The group's emergence shows how close New Jersey is to becoming the first state to enact a law that allows gay couples to marry, said Steven Goldstein, chairman of Garden State Equality, a gay civil-rights organization.

"We're ready for this battle," he said.

The only state that lets gay couples marry is Massachusetts - and that was because of a ruling from the state's top court.

Last year, New Jersey's Supreme Court declared that gay couples should have the same legal rights as married couples. The Legislature responded by adopting a civil unions law, which allows those benefits - but stops short of allowing gay couples to wed.

Goldstein and his allies have promised since then that they would keep pushing for full marriage. This time, he vowed, they would go to the Legislature first.

Just a year ago, it seemed a long shot that New Jersey lawmakers would pass a bill anytime soon. But civil unions have received poor reviews from couples, many of whom say their employers and others are not recognizing their new rights.

Nearly one-fifth of the more than 2,000 couples who had licenses for civil unions as of mid-November have complained to Garden State Equality that some of their rights have been denied.

Now, Goldstein said, he might have enough support to get a law passed. His group and another organization, Blue Jersey, have aired television commercials explaining their position.

Gov. Corzine has said he would sign a gay-marriage bill into law, but did not want to deal with the issue before the 2008 presidential election.