The Iowa Supreme Court on Friday struck down a decade-old law that barred gays from marrying, making the state the first in the U.S. heartland to allow same-sex marriages.

Opponents vowed to begin the difficult process of amending the Iowa constitution to overturn the ruling, while supporters said it may encourage other states to allow gay men and women to marry.

“We won. Not only that, it is unanimous and you are getting married,” said Camilla Taylor of Lambda Legal, speaking at a Des Moines hotel to the six same-sex couples who brought the original lawsuit in 2005. The news set off a round of cheers, tears and hugs.

The ruling makes Iowa the third U.S. state, after Connecticut and Massachusetts, that currently allows same sex couples to marry. California briefly allowed gay marriage, but rescinded it in a November 2008 referendum. The ruling leaves 43 states with laws explicitly prohibiting such marriages, including 29 with constitutional amendments restricting marriage to one man and one woman.

In the Iowa case, Varnum v. Brien, the couples sued Polk County Recorder of Deeds Timothy Brien for refusing to grant them marriage licenses.

A district court judge sided with the couples in August 2007, triggering a rush to the courthouse where one gay couple managed to get a license before the ruling was stayed.

The state supreme court affirmed that decision on Friday, declaring unconstitutional the 1998 Iowa Defense of Marriage Act that restricted marriage to one man and one woman.

The key principle at the heart of the case was the doctrine of equal protection under the law, which the court said “is essentially a direction that all persons similarly situated should be treated alike.”

HISTORICAL PRECEDENTS

The court compared the right of same-sex couples to marry with historical precedents that struck down slavery and segregation and recognized women’s rights.

“I think it’s significant nationally because you can’t say any more that this is something coming out of a coastal state with an overly liberal bias,” Drake University law professor Mark Kende said.

“People internationally will be struck by the fact that here is a heartland Midwestern state ruling in favor of gay marriage,” he said.

Susan Sommer, senior counsel with Lambda Legal in New York, which provided legal help for the lawsuit, said a number of states, including New York, Vermont and New Hampshire, have “very active efforts” under way to pass gay marriage provisions. Kende said Minnesota, Wisconsin and other heartland states with liberal traditions could follow.

California’s supreme court is hearing arguments about whether to re-legalize same-sex marriage after voters approved a ban in November, which set off national protests.

Iowa opponents of gay marriage were adamant they would fight on, and said they would pursue a constitutional amendment in the state legislature. The soonest such an amendment could be put before voters is 2012.

“This is just one step of many,” Baptist minister Keith Ratliff of Des Moines said. “It’s very important to all of us who are like-minded on this position that the things that have happened today do not stop us from believing what God has already ordained in dealing with marriage … so we just move forward.”

The court’s ruling said gay marriages in the state could take place beginning in three weeks.