WASHINGTON  The Nuclear Regulatory Commission on Thursday rejected all challenges to extending the operating license of the Vermont Yankee nuclear plant, setting up a confrontation between the reactor’s owner and the Vermont Legislature, which has blocked a state certificate needed to keep the plant running.

The commission voted 4 to 0, with one recusal, to allow its staff to issue the renewal. In a conference call with reporters, the commission’s chairman, Gregory B. Jaczko, said that the plant’s owner, Entergy, had met “all of our requirements and standards to be able to operate for another 20 years.” Still, operating the plant, in Vernon, Vt., on the Connecticut River near the Massachusetts line, requires “a variety of permits and other actions,” of which an N.R.C. license was just one, he said.

The state argues that the plant is too old to be reliable, an area over which it has jurisdiction.

In Vermont, environmentalism runs strong, and the plant has long been viewed with suspicion. A series of problems, including the collapse of a wooden cooling tower in 2007, leaks of tritium from underground pipes and denials by utility executives that there were such pipes, made the plant widely unpopular outside its immediate neighborhood.

Safety regulation rests with the Nuclear Regulatory Commission, but Entergy had signed a deal with Vermont in 2002 requiring the plant to get a “certificate of public good” from the state if the plant was going to operate beyond its initial 40-year license. All power plants in Vermont must have such a certificate.