DES MOINES, Iowa, (Reuters) – The Iowa Supreme  Court cleared the way for gay marriage in the state yesterday  by declaring a law that limits marriage to a man and a woman  unconstitutional. The ruling makes Iowa the third U.S. state after  Connecticut and Massachu-setts, and the first in the Midwest, to  allow gay and lesbian couples to marry.

Gay marriage was briefly legal in California, but voters  repealed it in a November 2008 referendum, though efforts are  under way to revive the issue.

The Iowa case, Varnum v. Brien, involved six same-sex  couples who sued the Polk County Recorder of Deeds Timothy  Brien in 2005 for refusing to grant them marriage licenses.

A county judge sided with the couples and the state supreme  court affirmed that decision and declared the 1998 Iowa Defense  of Marriage Act — which restricted marriage to one man and one  woman — unconstitutional.

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.”

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.

Susan Sommer, senior counsel with Lambda Legal in New York,  which sued in the Iowa case, said a number of states, including  New York, Vermont and New Hampshire, have “very active efforts”  underway to pass gay marriage provisions.