Gay rights attorneys are closely scrutinizing today’s Supreme Court ruling striking down the Defense of Marriage Act for clues on how the court might rule on future challenges to state laws barring gay marriage. And they think they’ve found a key tell that’s grounds for real optimism.

Buried in the decision is a reference to the Supreme Court’s decision in Loving v. Virginia, in which the Court struck down a state law against interracial marriage as unconstitutional. To gay advocates, the reference looks as if it could signal a readiness on the Court’s part to do the same to state laws banning gay marriage.

The reference to interracial marriage comes in a section where the majority opinion is discussing the validity of federal intervention in the traditional authority states have had over marriage. It says:

In order to assess the validity of that intervention it is necessary to discuss the extent of the state power and authority over marriage as a matter of history and tradition. State laws defining and regulating marriage, of course, must respect the constitutional rights of persons, see, e.g., Loving v. Virginia, 388 U.S. 1 (1967); but, subject to those guarantees, “regulation of domestic relations” is “an area that has log been regarded as a virtually exclusive province of the States.” Sosna v. Iowa, 416 U.S. 393, 404 (1975).

Gay rights lawyers see this seemingly subtle reference as potentially having far reaching significance. That’s because they have long cited Loving v. Virginia, a landmark civil rights case, as a key precedent for striking down Prop 8, the California law that defined marriage as between a man and a woman.

In Loving v. Virginia, the Supreme Court ruled that the Virginia law outlawing interracial marriage was unconstitutional on the grounds that it violated the equal protection clause in the Fourteenth Amendment, ruling that the freedom to marry must not be limited by discrimination and that the Virginia law had no legitimate purpose other than maintaining discrimination. That’s exactly the argument that lawyers for the plaintiffs in the Prop 8 case made in asking the Court to strike that law down.

Today the Court declined to take a position on Prop 8, invoking standing issues. And it didn’t directly address the question of whether states could or couldn’t continue to refuse to marry gay and lesbian couples. It didn’t declare a constitutional right to marriage.

But today’s DOMA decision made an expansive case against discrimination based on sexual orientation, and more specifically, the citation of Loving v. Virginia could be an encouraging signal. The court explicitly cited the decision in Loving v. Virginia as the standard by which we should judge whether state laws defining marriage respect the constitutional rights of the individual. That, advocates believe, is a hint that the Court may be prepared to hold other state laws to the same standard.

“The fact that the Court specifically noted that federal constitutional provisions trump state law if they violate the rights of citizens — and cited Loving v. Virginia in the process — is significant,” Theodore Boutrous, a lawyer for the plaintiffs in the Prop 8 case, tells me. “We have contended all along that Loving requires restrictions on same sex marriage to be struck down for the same reasons. This plants a seed for the future.”

This — plus the fact that today’s SCOTUS decision struck down DOMA as a violation of the Constitution’s guarantee of equal protection and due process, all but guarantees that a wave of new lawsuits will be brought against state laws around the country barring gay marriage. One of these cases is bound to reach the Supreme Court (without standing issues getting in the way of a decision) some time in the near future. If advocates are right about the significance of the citation of Loving, today’s decision may have been an even better day than we know for the future of gay civil rights in America.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.