The decision by a federal appeals court in New York to invalidate the Defense of Marriage Act improves the already strong prospect that the US Supreme Court will take up the issue of gay marriage this term.

On Thursday, a panel of the Second US Circuit Court of Appeals voted 2 to 1 to declare a portion of the Defense of Marriage Act (DOMA) unconstitutional because the majority judges said it violates the right of same-sex married spouses in New York to equal protection.

The decision marks the second time in five months that a federal appeals court has struck down DOMA on constitutional grounds.

On May 31, the First Circuit in Boston ruled in favor of same-sex couples in Massachusetts, challenging what they argued was the discriminatory nature of DOMA in allowing heterosexual couples to enjoy full federal benefits while denying those same benefits to married couples who are gay and lesbian.

The Supreme Court is poised to soon consider whether to take up as many as six different appeals raising various challenges to DOMA. Adding another appeals court decision to that mix increases the prospect the justices will agree to decide the question.

In addition, the Supreme Court is also poised to consider whether to examine a Ninth Circuit decision striking down California’s Proposition-8 ban on same-sex marriages in that state.

Thursday’s Second Circuit decision is interesting in part because of the lineup of judges and the speed of their work. The opinion striking down the statute was written by Chief Judge Dennis Jacobs, an appointee of President George H.W. Bush, and was joined by Christopher Droney, an Obama appointee.

The dissent was written by Chester Straub, a Clinton appointee.

Argument in the case took place three weeks ago on Sept. 27. The majority opinion totals 43 pages, and the dissent, 40. Some federal appeals courts are known for their rocket docket, but the Second Circuit is generally not among them.

The fast opinion suggests the judges – like the parties in litigation – may have kept one eye on the Supreme Court throughout the process.

The Second Circuit decision drew praise from gay rights activists and supporters and criticism from opponents.

“Today’s ruling is the second by a federal appellate court and the 10th ruling in a row from judges appointed by presidents from Nixon to Reagan to George W. Bush, all agreeing that this disgraceful and discriminatory gay exception to the way the federal government treats married couples must end,” said Evan Wolfson, president and founder of Freedom to Marry.

“The Supreme Court should swiftly agree to hear one or more of these cases and definitively strike down the so-called Defense of Marriage Act,” he said in a statement.

“Supporters of equality have a great deal to celebrate today,” says a statement from the liberal Center for American Progress. “The fact that this decision came from such a conservative judge makes it all the more likely that the Supreme Court will ultimately strike down the Defense of Marriage Act.”

Brian Brown, president of the conservative National Organization for Marriage, agreed that the decision points up the need for the Supreme Court to enter the fray. But he’s expecting a different outcome.

“This is yet another example of judicial activism and elite judges imposing their views on the American people,” Mr. Brown said in a statement. “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,” he said.

The Second Circuit case involves a challenge to the federal estate tax by Edith Windsor of New York City. Ms. Windsor and Thea Spyer were married in 2007 in Canada.

Their same-sex marriage was recognized under New York law, but after Ms. Spyer’s death in 2009, Windsor was denied the spousal waiver from the federal estate tax. She was forced to pay $363,000 that the surviving spouse in a heterosexual marriage would not have to pay.

The reason was DOMA, a law passed in 1996 that defined marriage for purposes of federal benefits as a “legal union between one man and one woman as husband and wife.”

Supporters of the law say it is a justifiable effort by Congress to direct federal benefits in a way that supports and encourages the traditional family unit with a mother and father caring for their own children.

Opponents of the law say DOMA discriminates against same-sex married couples and is not substantially related to an important government interest.