In a big win for gay rights and common decency, a federal appeals court has pronounced Proposition 8 unconstitutional, arguing that there’s no “legitimate reason for the passage of a law that treats different classes of people differently.”

There were two money quotes in the ruling. First, this: “Proposition 8 serves no purpose, and has no effect, other than to lessen the status and human dignity of gays and lesbians in California, and to officially reclassify their relationships and families as inferior to those of opposite-sex couples.” And second, the court shot down the reprehensible effort by Prop 8 supporters to argue that the Judge on the case was biased because he is gay, claiming there is no evidence for the claim.

So here’s an interesting angle on the decision: Gay rights advocates are hoping that this increases pressure on Obama to come out and unequivocally declare his support for gay marriage. He has said his position on it is “evolving.”

But one expert I spoke to points out that in fact, Obama has caught a pretty big break on this topic. That’s because the court’s ruling was narrow, and in effect actually affirms Obama’s position.

According to Richard Socarides, a prominent gay rights advocate, the key to the ruling is that it didn’t pronounce gay marriage a right under the U.S. Constitution. That broader ruling is what advocates had hoped for — and Obama would have been expected to declare agreement with it.

Rather, Socarides notes, the court today simply affirmed that you can’t take away by referendum a right to marry that citizens already enjoy under state law. And this is consistent with Obama’s position on Prop 8.

“We were hoping for a very broad ruling that held that there was a right under the Constitution to same sex marriage,” Socarides tells me. “If the court had ruled on those grounds, there would have been more pressure for him to move forward with his evolution on this.”

“The decision today is fully consistent with the president’s previously stated position that states should not take away rights by initiative,” Socarides continued. “He can continue to say, `my views are evolving but I completely agree that states should not take away rights by initiative.’ On this decision, he caught a break. Whether he will be able to continue avoiding the issue is still to be determined.”

Socarides says he doesn’t expect the decision to come before the Supreme Court this year.

Obama has done a great deal for the cause of gay rights, and he has left the clear impression that he fully supports gay marriage, even if he has not been willing to say so out loud. This has only stoked a desire among gay rights advocates for Obama to come clean about his true beliefs. But even if today’s decision doesn’t put any more pressure on him to do this, Obama can point to it to reaffirm, with real conviction, his oft-stated position that the arc of history bends slowly, but it bends towards justice.