Enforcement of decisions may well be delayed while the Supreme Court takes one or more of them for review, with a decision then possible by June 2015.
But if the Supreme Court demurs, those rulings will become law throughout those circuits, requiring many more states to join the 17 that have authorized same-sex marriage.
"This is the penultimate act," Michael C. Dorf, a constitutional expert at Cornell University Law School, said of the sudden wave of federal court hearings. It will start in Denver in April as the 10th U.S. Circuit Court of Appeals considers rulings that overturned marriage limits in Utah and Oklahoma.
Like many other legal scholars, Dorf predicts that same-sex marriage proponents will win many of the circuit-level decisions, which are generally handed down by three-judge panels.
Since June, when the Supreme Court required the federal government to recognize married same-sex couples and suggested that discriminatory laws were rooted in nothing but prejudice, rights advocates have won an uninterrupted series of decisions in federal district courts. Restrictive amendments or laws have been declared unconstitutional in Utah, Oklahoma, Virginia, Texas and Michigan, and partial decisions, requiring states to recognize out-of-state marriages, have been handed down in Kentucky, Ohio and Tennessee.
But most of these decisions have been stayed pending appeals, and the next chapter promises to be more momentous. Several of the appeals are on a fast track in circuit courts.
In addition to the Denver hearings next month, the 4th Circuit, based in Richmond, will hear arguments in the Virginia case in May. These cases are likely to be decided by summer or fall.
In other regions, hearings have not yet been scheduled but are considered very likely this year in the 9th Circuit, in San Francisco, regarding a 2012 decision that upheld Nevada's restrictive law. They also could occur this year in the 5th Circuit, in New Orleans, for the Texas case, and in the 6th Circuit, in Cincinnati, for cases from Michigan, Ohio and Kentucky.
Given the consistency of recent court decisions and the signals given by the Supreme Court in its ruling in June, many experts predict that some, if not most, of these circuit panels will uphold marriage rights for gay and lesbian couples. That could upend law in many conservative states.
The 10th Circuit, for example, includes Wyoming and Kansas, while the 4th Circuit includes North Carolina, South Carolina and West Virginia.
Given the potential wider impact of circuit decisions, pressure will be intense on the Supreme Court to address the issue head-on rather than skirting it as it did last year, when it allowed a decision overruling California's ban on same-sex marriage to stand on grounds that did not apply to other states in the 9th Circuit.
The Supreme Court will be all but forced to decide if, as appears possible, different circuits reach clashing conclusions. The one most likely to decide against same-sex marriage, many experts say, is the 5th Circuit, which will decide the Texas appeal. That circuit includes Mississippi and Louisiana, and the court is viewed as largely made up of conservative judges.
The Supreme Court's term runs from October to June. With the high likelihood that at least one circuit will decide against state limits by summer or fall, observers say, the Supreme Court should have ample time to hear a case for a decision by June 2015, though unexpected delays could push it to 2016 at the latest.
Even as drama unfolds at higher judicial levels, more than 50 challenges to marriage limits are working their way through lower federal courts and state courts. In the next three months, federal district courts will hear challenges in Idaho, Oregon and Pennsylvania, said Gary Buseck, legal director of Gay and Lesbian Advocates and Defenders.
These or other cases may yield still more of the circuit-court decisions that can have a multiplier effect regionally, or help propel the issue onto the Supreme Court docket.
If, despite recent signs, the Supreme Court finds no constitutional right to same-sex marriage, that could block such marriages in states like Utah and Virginia, where laws were overturned by federal courts. But it would not turn back the clock in the 17 states that adopted same-sex marriage on their own through legislation, ballot questions or state court decisions.