“WHITE PLAINS, Oct. 29 – The Nuclear Regulatory Commission has granted permission to the owners of the Indian Point nuclear power complex to increase output at one of its reactors by 3.3 percent.

The agency, which approved the increase in capacity, or “uprate,” on Thursday, based its decision on a determination that the plant could safely increase output primarily by upgrading minor components, a commission spokesman said on Friday.

The agency had published a notice about the uprate application in the Federal Register, inviting opponents of the plant to request a hearing or file a comment challenging an increase, but no one intervened, said the spokesman, Neil Sheehan.

Alex Matthiessen, the executive director of Riverkeeper, an environmental group that has sought to shut down Indian Point’s two operational reactors, said he chose not to protest the application. “We didn’t have the staff time to devote to it,” he said Friday. “You have to pick your battles.”

Safety experts have questioned the nuclear industry’s use of uprates to increase capacity at existing plants. In the past two decades, total output nationally has been increased by the equivalent of three large reactors without building any new plants.

Mr. Sheehan said that since 1977, the commission had approved 101 power upgrades of between 1 and 20 percent at nuclear power plants in the United States.

They have been granted with almost no opposition, though critics contend that the uprates, on top of extensions of operating licenses, could imperil safety.

The Indian Point 2 reactor, the one that received uprate approval last week, had three unplanned shutdowns in September because of equipment malfunctions, said a spokesman for Entergy Nuclear Northeast, the plant’s owner.

“When you increase capacity to these plants, you are no doubt adding pressure on the existing facility,” Mr. Matthiessen said.

But plant owners and regulators contend that they are modernizing in a way that improves safety.

Entergy plans to put the increase into effect after the plant’s fall refueling operation, which is currently under way, Mr. Sheehan said.

The last uprate at Indian Point 2, of 1.4 percent, was in 2003; its sister reactor, Indian Point 3, received an uprate of 1.4 percent in 2002. An application to increase the capacity of Indian Point 3 by 4.85 percent is being reviewed. Indian Point 1 closed in the 1970’s.”