Topeka ? Federal courts ultimately will strike down an amendment to the Kansas Constitution banning gay marriage and similar measures in other states, the leader of a group favoring such prohibitions predicted Wednesday.

“All these state amendments are going to be struck down by federal judges,” said Matt Daniels, president of the Alliance for Marriage. “We’re in a race now — in a race between the democratic process in Kansas and other states and the federal courts.”

Daniels’ group has proposed an amendment to the U.S. Constitution to define marriage as a union between one man and one woman but leave to the states other issues, such as permitting civil unions. He said such a federal amendment is necessary to head off legal challenges to state amendments.

Meanwhile, Matt Foreman, executive director of the National Gay and Lesbian Task Force, agreed that the U.S. Supreme Court ultimately will determine the validity of state constitutional bans on same-sex marriage.

“Eventually, the Supreme Court is going to have to decide what the U.S. Constitution says about this issue,” Foreman said.

With final, unofficial results from Tuesday’s balloting from 104 of Kansas’ 105 counties, 414,235, or 70 percent, voted “yes,” and 178,167, or 29 percent voted “no.”

The amendment reaffirms the state’s long-standing policy of recognizing only marriages between one man and one woman. But it also declares that only such traditional unions are entitled to the “rights and incidents” of marriage, prohibiting the state from authorizing civil unions for gay couples.

Kansas became the 18th state with a gay-marriage ban in its constitution, and voters in Alabama, South Dakota and Tennessee will consider similar questions next year.

Before Kansas’ election, some critics had predicted adoption of its amendment would result in a federal court challenge. Such a challenge is under way in Nebraska, where voters approved an amendment in 2000 and critics argue that it violates gays’ and lesbians’ right to seek policy changes from legislators.

Some supporters of the Kansas amendment saw a federal lawsuit as unlikely, but Daniels was confident one would occur, arguing gay rights activists have turned to the courts in recent years because they haven’t made enough progress with legislators and voters toward legalization of same-sex marriages.

“You’re going to see the courts slap the American people in the face,” Daniels said during an interview, calling arguments in Nebraska and elsewhere against such bans “false.”

But David Buckel, director of marriage-related activities for the New York-based gay rights group Lambda Legal, said groups like his don’t go to court lightly. Lambda Legal and the American Civil Liberties Union are challenging Nebraska’s amendment.

“We do not assume that we’re running into court in each and every instance, because we want to win,” Buckel said.