The Nuclear Regulatory Commission has sent a bulletin to the nation's atomic power plants alerting owners of an increase in acts of "insider" sabotage by employes, it was learned yesterday.

"It is not a mushrooming crime wave or anything," said Edward L. Jordan of the NRC office of inspection and enforcement. But he said the NRC is receiving more reports of "deliberate acts directed against plant equipment in vital areas" than it did three or four years ago.

In a bulletin sent to atomic power plants May 4, the NRC said plant managers are "not totally prepared" to deal with some of the situations arising recently from insider sabotage.

While the bulletin did not itemize instances of such sabotage, NRC Chairman Nunzio J. Palladino, in a February letter to Rep. Edward J. Markey (D-Mass.), said 11 incidents had been "directed against plant equipment in vital areas at operating nuclear power stations" in the past three years.

These incidents involved such acts as cutting control wires, dumping metal chips into the lubricating oil of reactor coolant pumps and tampering with valves in a way that allowed release of radioactive gas into the atmosphere.

The NRC bulletin warned that the potential for acts of this kind by employes "must be recognized," and told the owners they must be ready to decide quickly whether "continued operation is justified and whether systems necessary for a safe shutdown are operable."

"They should develop procedures that cover these types of situations so they don't ad hoc improvise a solution in the middle of the night," Jordan said.

The problem of insider sabotage, acts by one or more workers that could disable an atomic reactor and possibly threaten the safety of the public, has worried a number of nuclear regulators for many years.

The NRC's Advisory Committee on Reactor Safeguards repeatedly has urged the commission, which long has focused on dealing with external threats to atomic power plants, to devote more attention to "sabotage by insiders."

But the NRC has shied away from using the word "sabotage" to describe any of the many insider incidents that have occurred in plants.

"The NRC seems to be reserving the word 'sabotage' for the eventuality of a successful attack which causes a major radioactive release," Markey said. "They historically haven't taken this problem seriously enough, and they still aren't taking it seriously enough."

Jordan acknowledged that over the years there have been a number of events at atomic power plants "that were difficult to explain, which one expects may have been an act of defiance or to aggravate the staff or for whatever purpose." However, he said that none could be called "an overt act of sabotage."

Many of these, he said, stemmed from "labor problems, a personal grudge type of thing or a grudge against a utility."

"No serious plant event has occurred as a result of these acts," he said. "But there has been equipment made inoperable so that the probability of an event--given some other things--was increased, so the risk to the public was increased slightly."

Two examples cited by the NRC bulletin illustrate the risk that insider sabotage can pose.

The first involved the Salem atomic power station in southern New Jersey, which two weeks ago was given permission to restart following a February incident termed the most serious safety mishap since the Three Mile Island accident in 1979.

The NRC said that on May 1, 1982, instrument valves were "apparently deliberately mispositioned" in a way that knocked out the steam generator feedwater pump, forcing the operator to reduce power immediately to keep the reactor from going into an emergency shutdown.

"The licensee plant owner concluded that this deliberate act could have been the result of a labor dispute," the bulletin said.

The second illustration cited by the NRC took place at the Beaver Valley plant near Pittsburgh on June 5, 1981, where a valve normally locked in an open position was found shut, and "the chain and padlock which secured this valve in the open position were missing."

With the valve shut, emergency cooling water would not have been available for high-pressure injection into the core in the event of an emergency, according to the NRC. Palladino told Markey that even though no arrest has been made and there is no suspect, the NRC believes that the motive for the incident was harassment of the utility rather than sabotage.