A reactor at the nuclear power plant in Browns Ferry, Ala., was shut down automatically three times last month, and nine plant employes were suspended during an FBI investigation of the incidents, the Tennessee Valley Authority disclosed yesterday.

Seven of the nine employes have been cleared, a TVA spokesman said. A preliminary FBI investigation that started Wednesday has uncovered no indications of a federal crime, such as sabotage or fraud, an FBI spokesman said.

A nuclear power plant has numerous places from which operations can be halted. "You can kick a piece of equipment, like an electrical panel, hard enough to make the plant trip," a TVA source said. "Trip" is a term used to describe a shutdown of the nuclear reactor and the generating equipment powered by the reactor.

The reactor tripped off last month is one of three units at the TVA facility in Alabama. One of the reactors already was shut down for normal maintenance, and temporary workers had been hired for that job. Temporary employes were among those initially suspended and questioned by the FBI about the unexplained shutdown of the second reactor.

The unit shout down for eight hours on Feb. 10, eight hours on Feb. 12 and again on Feb 15. After the third incident, plant officials decided to keep the unit closed for testing and for some previously scheduled repairs.

"We didn't find anything mechanical or operational to explain the trip," a TVA spokesman, John Schlatter, said at the agency's headquarters in Knoxville, Tenn.

The reactor was returned to service last Monday, and on Wednesday the plant superintendant asked for the FBI investigation. The TVA did not indicate why he asked for the security check. The nine workers were suspended Thursday.

TVA officials would not reveal the names or the jobs of the suspended workers.

In another recent security incident at Browns Ferry, a woman employe mistakenly carried a pistol into the plant in her purse. She notified her supervisor and was not suspended. The TVA did not explain how the pistol escaped discovery by metal detectors and other screening devices. The employe usually keeps the pistol with her off the job, and forgot to remove it from the purse that she took to the plant that day.

At the TVA Sequoyah plant in Soddy -Daisy, Tenn., an employe was suspended for taking pictures without permission last Saturday when loading of uranium fuel started. Ironically, the loading was filmed by television crews and photographers.

The employe was suspended because he took pictures even after his request to do so was denied, a spokesman said.