Carol Schall, left, and her partner, Mary Townley, were married in California in 2008 and have joined a lawsuit challenging Virginia's ban on same-sex marriage. Almost overnight, Virginia has emerged as a critical state in the nationwide fight to grant gay men and women the right to wed. (Steve Helber/AP)

The race to get the Supreme Court to decide whether it is unconstitutional for states to ban same-sex couples from marrying may run through Virginia.

Two lawsuits filed on opposite sides of the commonwealth are among dozens nationally that challenge state laws and constitutional amendments that limit marriage to a union between a man and a woman. But the Virginia cases are moving quickly, and some lawyers hope they will emerge through the appeals process as favored vehicles for an ultimate decision by the Supreme Court.

The impact of a lawsuit brought by American Civil Liberties Union lawyers in Harrisonburg on behalf of four lesbians increased Friday when U.S. District Judge Michael F. Urbanski ruled that it should be expanded into a class-action suit covering Virginia’s estimated 15,000 same-sex couples who might want to marry.

And in a courtroom just over 200 miles away in Norfolk on Tuesday, U.S. District Judge ­Arenda L. Wright Allen will consider for the first time Virginia’s startling reversal of the commonwealth’s legal position on same-sex marriage.

Virginia’s new attorney general, Mark R. Herring (D), said two weeks ago that the state’s ban, which voters approved in 2006, is unconstitutional and cannot be defended. Herring infuriated Republican lawmakers by joining two gay couples in asking Wright Allen for a decision that, as he wrote in a brief, “will be a landmark ruling in Virginia on one of the most important civil rights issues of our time.”

The Norfolk case is on a fast track, and that was a lure for the American Foundation for Equal Rights, whose celebrity lawyers, Theodore B. Olson and David Boies, have joined the suit. They won their battle to overturn California’s Proposition 8 and return same-sex marriage to the state, but the Supreme Court stopped short of reaching the question of whether states may ban such unions.

They are hoping that Wright Allen’s decision — and the prospect of a speedy review by the U.S. Court of Appeals for the 4th Circuit, based in Richmond — will allow them to make the case again before the Supreme Court.

But there are plenty of other candidates: James Esseks of the ACLU’s Lesbian, Gay, Bisexual, Transgender and AIDS Project said 47 cases in federal and state courts are challenging same-sex marriage bans in 24 of the 33 states that have them.

“No one knows where the next decision might come from,” Esseks said. None of the cases will reach the high court for consideration in its current term, which ends in June. And none have been reviewed by appeals courts.

When the Supreme Court handed supporters of same-sex marriage historic victories in June, it consciously stopped short of answering a fundamental question: whether there is a constitutional right to marriage that states may not deny to gay couples.

But the expansive language of the five-member majority’s opinion invalidating a key part of the federal Defense of Marriage Act (DOMA) nonetheless has proved a boon to activists pursuing that goal.

In the seven months since the court’s decision, state supreme courts and federal judges have used the court’s reasoning to strike down state bans and to require greater scrutiny for laws and rules that single out people because of their sexual orientation.

The Supreme Court’s ruling in United States v. Windsor is confronting judges with a paradox. On the one hand, the opinion written by Justice Anthony M. Kennedy and joined by the court’s four liberals noted that defining marriage is traditionally a power reserved for the states.

On the other, the opinion dismissed Congress’s arguments as to why the federal government should recognize only traditional definitions of marriage. It said the arguments were mostly window dressing for unlawful prejudice based on sexual orientation.

State courts and federal judges have embraced that latter reasoning to trump the rights of states, and bans on same-sex marriage have been found unconstitutional since June in New Jersey, New Mexico, Oklahoma and Utah. The Utah and Oklahoma decisions are being appealed to the U.S. Court of Appeals for the 10th Circuit, based in Denver.

In effect, said William Baude, a law professor at the University of Chicago who follows the issue, the majority’s language in Windsor has been viewed as “permission” for judges “who might already have been inclined” to believe there is a constitutional right to marry.

If the opinion’s words offered a sort of dog whistle for lower courts about the Supreme Court’s ultimate direction, Senior U.S. District Judge Terence C. Kern of Tulsa seemed to think he heard it.

He noted in considering Oklahoma’s ban that the justices have not “expressly reached the issue of whether state laws prohibiting same-sex marriage violate the U.S. Constitution.”

But he said that had to be balanced with a string of rulings — all of them written by Kennedy, the justice most often in the middle in ideological battles on the court — beginning with an important decision on gay rights, Romer v. Evans, decided 17 years ago.

“Supreme Court law now prohibits states from passing laws that are born of animosity against homosexuals, extends constitutional protection to the moral and sexual choices of homosexuals, and prohibits the federal government from treating opposite-sex marriages and same-sex mar­riages differently,” wrote Kern, who was appointed to the bench in 1994.

“There is no precise legal label for what has occurred in Supreme Court jurisprudence beginning with Romer in 1996 and culminating in Windsor in 2013, but this court knows a rhetorical shift when it sees one.”

No lower court has taken the lesson of Windsor to be that state bans should be upheld, but it is a small universe so far.

U.S. District Judge Timothy S. Black has ruled that Ohio must recognize a same-sex marriage performed elsewhere on a death certificate when one of the spouses dies.

And in December, U.S. District Judge Robert J. Shelby in Salt Lake City became the first federal judge to use Windsor to strike down a state ban on same-sex marriage. More than 1,300 couples married before the Supreme Court stepped in to stay the decision while the state of Utah appealed it. The court gave no reason for the stay.

The decisions have come from judges appointed by Democratic presidents, as were Wright Allen and Urbanski.

Ken Connelly, whose organization Alliance Defending Freedom has intervened in the Norfolk case to defend Virginia’s law, said the handful of cases decided in the aftermath of Windsor are simply wrong.

“There are plenty of rational reasons for states to adopt the time-tested definition of marriage” as that between a man and a woman, Connelly said. The importance of Windsor was the court’s recognition of a state’s role in making that definition, he said.

Connelly’s group is representing Prince William County Circuit Court Clerk Michèle B. McQuigg and adopting the arguments of former state attorney general Ken Cuccinelli II (R) about Virginia’s interest in promoting traditional marriage to encourage offspring to be raised by two parents, among other goals. Virginia’s voters approved the constitutional amendment in 2004, although some recent polls have shown that a majority now endorse same-sex marriage.

Esseks counters that Virginia has not advanced a reason for the ban that five members of the Supreme Court have not already dismissed.

“The stated reasons Virginia offers end up being the same ones trotted out by the House to justify DOMA, and the court said they had no rational relationship to a legitimate state interest,” Esseks said.

One appeals court has used the Windsor decision to potentially even broader effect. A unanimous panel of the U.S. Court of Appeals for the 9th Circuit, in California, said the Supreme Court’s language implied that treating people differently because of their sexual orientation required greater justification than usual.

The case involved the dismissal of a prospective gay juror. But the legal command of “heightened scrutiny” makes it less likely that the government can prevail when defending laws that treat people differently because of their sexual orientation.

That would seem to put at risk same-sex marriage bans in Western states covered by the 9th Circuit. For instance, a federal judge upheld Nevada’s ban in 2012. But Nevada Attorney General Catherine Cortez Masto (D) said the 9th Circuit’s ruling, if not overturned, will cause her to rethink whether the state can continue to defend the law on appeal.