WINTERSBURG, Ariz. (AP) _ Officials at the Palo Verde Nuclear Generating Station said they have begun their fifth investigation since July of possible sabotage.

The U.S. Nuclear Regulatory Commission was notified Thursday that the plant is studying an incident in which two wires were cut in an instrument panel in the control room of Unit 3, which is under construction.

The wires were connected to an instrument that monitors the amount of water flowing to a spray pond beside the unit, said Dan Canady, a plant spokesman.

The damage was discovered Tuesday, he said.

''It's too early to tell whether the snipped wires were deliberately cut or if it was accidental,'' he said.

Although Unit 3 is 99 percent complete, that area of the triple-reactor plant still is open to construction workers, Canady said.

The spray pond is used to help cool the plant after it has been shut down, he said, and damage to the measurement device would not be serious, because of backup systems.

Plant personnel are conducting the investigation, and no law-enforcement agencies have been notified, Canady said.

Investigations have been conducted into four incidents at the plant since July. But plant operators said they could not find enough evidence to determine whether the problems were caused by accidents or sabotage.

Three incidents in Unit 2 involved switches being flipped. The fourth, in Unit 3, involved rags being stuffed into an electrical breaker and paper being placed into tracks that connect to a breaker box.

In February 1984, $150,000 worth of electrical cables were cut.

The plant, 50 miles west of downtown Phoenix, is owned by a consortium of electric utilities in Arizona, New Mexico, Texas and California.