WASHINGTON - Gay-rights advocates won another victory in their fight for equal treatment under law Thursday, when the U.S. appeals court in New York struck down a key part of the Defense of Marriage Act and held for the first time that gays and lesbians are a minority group deserving of special protection from discrimination under the Constitution.

The 2nd Circuit Court of Appeals in Manhattan joined a growing number of federal judges who have ruled that the U.S. government may not deny equal federal benefits to legally married gay couples.

But in its opinion Thursday, the 2nd Circuit broke new ground, becoming the first to decide that official discrimination against gays and lesbians is like discrimination against women or racial minorities and generally forbidden by law.

"Homosexuals have suffered a history of discrimination," said Chief Judge Dennis Jacobs for a 2-1 majority. And while gays and lesbians have been winning political victories, he said they are still subject to many discriminatory laws. Jacobs said courts should view all laws that discriminate based on sexual orientation with the same skepticism accorded to laws that discriminate based on gender.

Case brought by widow

Jacobs, who has a generally conservative reputation, was appointed to the court by former President George H.W. Bush. He was joined by Judge Christopher Droney, an appointee of former President Bill Clinton. In dissent, Judge Chester Straub, a Ronald Reagan appointee, said judges should not change the traditional definition of marriage.

The judges ruled in the case of Edith Windsor, 83, a widow who had to pay $363,000 in federal estate taxes after the death of her spouse, Thea Spyer, because under federal law they were not legally married. The two met in New York's Greenwich Village in the 1960s and were together for 44 years. Windsor, a programmer with IBM, and Spyer, a psychologist, married in Canada in 2007 and lived in New York, one of six states where same-sex marriage is legal.

'It is only right'

"Edie and Thea's home state of New York ... explicitly supports the freedom to marry," said Mariko Hirose, an attorney with the New York Civil Liberties Union. "It is only right that the federal government respect the state's decision and treat all married couples fairly."

When Congress passed DOMA in 1996, its main goal was to protect states from being forced to honor same-sex marriages from other states. That part of the law still stands. The decision Thursday rejects another part of the law that bars federal agencies from recognizing same-sex couples, even in states where their marriages are legal.

Married couples from Massachusetts, Connecticut, California and New York have filed suits to challenge this provision. They argued they were being wrongly denied the tax benefits and Social Security survivor payments as well as family health insurance that is available to other married federal employees. And in every recently decided case, they have won. The judges have said this anti-gay discrimination violates the Constitution's guarantee of equal protection of the laws. They have also noted that marriage has been a matter of state law, not federal law.

President Obama said last year that his administration would not defend DOMA in court. House Republicans then hired Washington attorney Paul Clement, a former solicitor general under President George W. Bush, to the argue for the law's constitutionality. The Supreme Court is expected to take up one or more of the cases this year.