BOULDER, Colo. — County clerks like Hillary Hall tend not to be bomb throwers. “We’re procedural, and we’re cautious,” she said, noting that clerks are duty-bound to follow bureaucratic rules for counting ballots, recording property deeds and registering license plates.

But last week, after a federal appeals court struck down Utah’s ban on same-sex unions, Ms. Hall decided the time had come to start issuing same-sex marriage licenses in Colorado, where they are not allowed. The move drew 97 delighted couples to the clerk’s offices, but it also put this liberal college town in the Rocky Mountain foothills on a potential collision course with the state’s Republican attorney general, John Suthers.

Mr. Suthers’s office urged Ms. Hall to stop issuing licenses for same-sex marriages and warned of “further action” if she did not. He warned that the unions were invalid under Colorado’s Constitution, which limits marriage to one man and one woman. The United States Court of Appeals for the 10th Circuit in Denver, which struck down Utah’s ban, had also stayed its decision, Mr. Suthers pointed out. That meant its judgment had not gone into effect in Utah, he said, “let alone in Colorado,” which is in the jurisdiction of the same appeals court.

Mr. Suthers’s office said it would be willing to ask the Colorado Supreme Court for a ruling on whether Boulder had the authority to marry same-sex couples. But it said the marriages must end first.