A number of nuclear power plants could be vulnerable to earthquakes because they were not built the way they were designed, the Nuclear Regulatory Commission staff reported yesterday.

The NRC immediately voted to issue an order today telling all utilities to check plants within the next 120 days and report whether they are built to specifications.

NRC staff member William Russell, who chaired a special task force on seismic analysis, said 10 plants had been found to have "significant differences between the original design and the 'as built' condition of the piping systems."

Virginia Electric and Power Co.'s Surry I plant, for example, he said, showed nine instances of high pipe stress and seven were the result of mislocated supports, supports of the wrong type or mismatched pipes.

The Surry I plant and four others, including Surry II, were shut down March 13 because of the faulty piping, but the reason the NRC gave at the time was that an erroneous computer formula had been used to build the plants.

It turned out in the staff analysis, Russell said, that although the formula was indeed faulty, "its significance was not as great as originally perceived. Other factors contributed to the large stresses we saw."

The same factors, including construction errors, could affect many of the nation's 70 licensed reactors, he said: "This is possibly only the tip of the iceberg."

Only one of the Surry I pipe problems resulted from the faulty computer code, Russell continued. Although Vepco had asked permission earlier to reopen Surry I, the new findings will delay its startup at least until September.

A Vepco spokesman said there would be no comment until utility officials had more information on the NRC findings.

The Surry II plant is shut down to repair its steam generator and has not yet begun looking at any piping problems, Russell said. Maine Yankee was restarted May 24 and analysis is continuing at the two remaining plants closed in March for pipe stress: Beaver Valley near Pittsburgh, Pa., and Fitzpatrick at Scriba, N.Y.

Both Beaver Valley and Fitzpatrick reported problems similar to those at Surry I. "The as-built conditions differ significantly firm the original design," the Beaver Valley unit said.

Other units reported that supports were the wrong size, in the wrong location or totally different from the way they were designed. Some support were missing parts or were missing altogether.

The Union of Concerned Scientists, a Massachusetts-based group critical of nuclear power, had petitioned the NRC to shut down the nation's nuclear plants pending a review of earthquake-proofing measures. Russell said that although that petition had not been formally acted upon, many of the actions ordered today were the same ones the UCS has requested.