Two nuclear plants in New York and Nebraska with good performance re-cords are being added to the list of the nation's worst because of concerns that their operators can't handle things that aren't routine.

By the same token, good performance in the face of the unexpected has led the staff of the Nuclear Regulatory Commission to take a Colorado plant off the list.At the Nine Mile Point No. 1 plant in Scriba, N.Y., "The principal areas of concern (are) the ability of the organization to identify problems, correct them and implement successful solutions," said William Kane, regional director of reactor programs, in a briefing for the commission on Wednesday.

At the Fort Calhoun plant in Nebraska, the staff concerns have to do "not with the operating performance of the plant, which sets records and operates exceedingly well," but with "the depth of their ability to withstand complex challenge when it occurs," said Robert Martin, regional administrator based in Arlington, Texas.

The listing, now 16 reactors at 10 sites, means the plants get special surveillance and the owners generally have to show they can operate safely.

Special concern is no longer warranted for the Fort St. Vrain plant Public Service Co. of Colorado near Denver, which has suffered frequent breakdowns since it was built in 1979, the staff said.

"Over the last six months, their performance has demonstrated to us a good approach to the handling of issues," said Martin.

The New York plant, on Lake Ontario, is 19 years old and, before being forced out of service last December by feedwater problems, had recently run for 420 days without a shutdown.

This long run could have made the owner, Niagara Mohawk Power Corp., complacent, the staff said.

A good response to challenge is one reason the Colorado plant no longer needs special supervision, said Martin. Inspections have shown "a good operational work ethic," Martin said.