NEW YORK » Saying the gay population has “suffered a history of discrimination,” a divided federal appeals court in Manhattan ruled today that a federal law defining marriage as a union between a man and a woman was unconstitutional, adding fuel to an issue expected to reach the U.S. Supreme Court soon.

The 2nd U.S. Circuit Court of Appeals seemed interested in adding its voice to several other rulings already at the high court’s doorstep by issuing its 2-to-1 decision only three weeks after hearing arguments on a lower court judge’s findings that the 1996 law was unconstitutional.

In a majority opinion written by Judge Dennis Jacobs, the 2nd Circuit, like a federal appeals court in Boston before it, found no reason the Defense of Marriage Act could be used to deny benefits to married gay couples. It supported a lower court ruling after a woman sued the government in 2010, saying the law required her to pay $363,053 in federal estate tax after her partner of 44 years died.

Jacobs, though, went beyond the Boston court, saying discrimination against gays should be scrutinized by the courts in the same heightened way as discrimination faced by women was in the 1970s. At the time, he noted, they faced widespread discrimination in the workplace and elsewhere. The heightened scrutiny, as it is referred to in legal circles, would mean government discrimination against gays would be assumed to be unconstitutional.

“The question is not whether homosexuals have achieved political successes over the years; they clearly have. The question is whether they have the strength to politically protect themselves from wrongful discrimination,” said Jacobs, who was appointed to the bench in 1992 by President George H.W. Bush.

He said it was difficult to say whether gays were under-represented in positions of power and authority without knowing their true numbers.

“But it is safe to say that the seemingly small number of acknowledged homosexuals so situated is attributable either to a hostility that excludes them or to a hostility that keeps their sexual preference private — which, for our purposes, amounts to much the same thing,” Jacobs said.

Lawyer Paul Clement, who had argued in support of the law on behalf of the Bipartisan Legal Advisory Group of the House of Representatives, was traveling and did not immediately return a message seeking comment.

Brian Brown, president of the National Organization for Marriage, which filed arguments with the appeals court before the ruling, called the decision “yet another example of judicial activism and elite judges imposing their views on the American people.”

He urged the Supreme Court to take up the case, saying: “The American people are entitled to a definitive ruling in support of marriage as the union of one man and one woman, as 32 states have determined through popular vote.”

Dale Schowengerdt, an attorney with the Scottsdale, Ariz.-based Alliance Defending Freedom, called the ruling “off base” and predicted the Supreme Court will disagree with it.

James Esseks, an attorney for the American Civil Liberties Union, called the ruling “a watershed moment in the legal movement for lesbian and gay rights.”

“It’s fabulous news for same-sex couples in New York and other states,” he said.

Senate Judiciary Committee Chairman Sen. Patrick Leahy, D-Vt., said the decision echoed testimony before his committee that showed the law “has damaging effects on the lives of thousands of American families who are denied the same federal protections as millions of other Americans.”

The 2nd Circuit said the law’s “classification of same-sex spouses was not substantially related to an important government interest” and thus violated the equal protection clause of the Constitution.

“It is easy to conclude that homosexuals have suffered a history of discrimination,” Jacobs said, noting that for many years in many states, homosexual conduct was criminal and that even the law’s supporters acknowledge that gays endured discrimination since at least the 1920s.

He said the law was written so broadly that it touches more than a thousand federal laws. “Homosexuals are not in a position to adequately protect themselves from the discriminatory wishes of the majoritarian public,” Jacobs wrote.

He rejected arguments by supporters of the law that it was intended to limit new categories of eligibility for federal funds, promote uniform administration of federal law, protect traditional marriage and encourage responsible procreation.

“Even if preserving tradition were in itself an important goal, DOMA is not a means to achieve it,” he said.

Jacobs disputed arguments that same-sex couples have a diminished ability to discharge family roles in procreation and the raising of children, saying the arguments were “inconsistent with actual cases.”

And in a footnote, he said that to the extent the law’s supporters contend that “Congress’ laws might actually influence sexual orientation, there is no evidence to support that claim (and it strikes us as farfetched).”

Judge Chester J. Straub dissented, saying that if the government was to change its understanding of marriage, “I believe it is for the American people to do so.”

“Courts should not intervene where there is a robust political debate because doing so poisons the political well, imposing a destructive anti-majoritarian constitutional ruling on a vigorous debate,” he said.

The ruling came in a case brought by Edith Windsor. She sued the government in November 2010 because she was told to pay $363,053 in federal estate tax after her partner of 44 years, Thea Spyer, died in 2009. They had married in Canada in 2007.

“This law violated the fundamental American principle of fairness that we all cherish,” Windsor said in a statement. “I know Thea would have been so proud to see how far we have come in our fight to be treated with dignity.”

The law, which denies federal recognition of same-sex marriages and affirms the right of states to refuse to recognize such marriages, was passed by bipartisan majorities in both houses of Congress and signed by President Bill Clinton after it appeared in 1993 that Hawaii might legalize gay marriage. Since then, many states have banned gay marriage but several have approved it, including Massachusetts and New York.

The government defended the federal law until President Barack Obama and Attorney General Eric Holder in early 2011 directed attorneys to stop doing so. A government lawyer told the 2nd Circuit that the administration reviewed the law and concluded that it deserved a stricter view of what constituted discrimination than the legal reasoning that had previously been applied.