TAMPA, Fla. — 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 lawsuit by two women seeking to have their Massachusetts marriage recognized here.

Attorneys for conservative groups hailed the ruling by U.S. District Judge James S. Moody as an important first step, but the plaintiffs promised to appeal.

"This is a legal shot heard 'round the world," said attorney Ellis Rubin, who filed the lawsuit on the women's behalf. "But we are not giving up. . . . This case is going to be resolved in the U.S. Supreme Court, and I have said that since the day I filed it."

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.

In Utah, a state constitutional amendment banning same-sex marriage and other "domestic unions" took effect Jan. 1.

Monte Stewart, president of the Utah-based Marriage Law Foundation, said the decision is encouraging even though he believes the constitutionality of DOMA will eventually be decided by the U.S. Supreme Court.

"Although traditional marriage has fared well in democratic processes, a number of judges have taken it upon themselves to radically redefine marriage," he said. "We always welcome victories in the judicial arena."

Scott McCoy, who headed up the Don't Amend Alliance campaign against the marriage measure, said the decision shows there was never any real danger that same-sex marriage would be judicially legalized in Utah without a constitutional amendment.

"It looks like the Defense of Marriage Act is sufficient for those (states) who don't want to recognize same-sex marriages," McCoy said.

McCoy acknowledged that the issue would likely end up in the U.S. Supreme Court, but "in the short term, all the conservatives' fears that gay marriage was going to spread like wildfire across the country, they are absurd."

The Louisiana Supreme Court, meanwhile, on Wednesday unanimously reinstated an anti-gay marriage amendment to the state constitution that was overwhelmingly approved by the voters in September.

The high court reversed a ruling by a state district judge, who struck down the "defense of marriage" amendment in October on the grounds that the measure dealt with more than one subject, in violation of the Louisiana Constitution.