TAMPA, FLORIDA — In what is believed to be the first ruling of its kind, a judge on Wednesday upheld the federal law letting states ban same-sex marriages, dismissing a suit by two women seeking to have their Massachusetts marriage recognized in Florida.

Lawyers for conservative groups hailed the ruling in U.S. District Court. The plaintiffs promised to appeal.

Although several federal cases are challenging the 1996 Defense of Marriage Act, attorneys said Wednesday’s ruling was the first by a federal judge on a direct challenge to the law.

Moody sided with departing Atty. Gen. John Ashcroft, who argued the government has a legitimate interest in allowing states to ban same-sex marriages, namely to encourage “stable relationships” for the rearing of children.

Elsewhere Wednesday, the Louisiana Supreme Court reinstated an anti-gay marriage amendment to the state constitution that was overwhelmingly approved by voters in September. The high court reversed a ruling by a state judge who struck down the “defense of marriage” amendment on grounds it dealt with more than one subject, in violation of the Louisiana Constitution.