An FBI official investigating the dumping of a corrosive substance into stored fuel elements at the Surry nuclear power plant said yesterday that sabotage is only one possible motive for the incident at the facility run by the Virginia Electric and Power Co. in southeast Virginia.

"It could have been a disgruntled employe or vandalism or a kook who has a funny idea about nuclear security," said Bill Ervin, an agent helping to run the Richmond office's Surry probe. He said the word sabotage is used by investigators to refer to a specific type of act affecting the national defense.

FBI agents went to the Surry site Tuesday, Ervin said, a day after Vepco officials discovered that a caustic white crystalline substance had been poured into 62 fresh fuels elements kept in storage at the plant. He called the investigation "a high priority case," but said no specific leads have been turned up.

At a news conference yesterday, Vepco officials said they had found no visible damage to any of the fuel elements, including the metal containers and zirconium rods holding the fresh fuel.

"An initial inspection by Westinghouse metalurgists shows no damage to the rods or to the fuel assemblage at all, but we will still have to test them," said Vepco spokesman Doug Cochran.

Although the crystalline substance has not yet been identified, Cochran said preliminary analysis shows it is a sodium caustic compound of the kind used in drain cleaners.

The Nuclear Regulatory Commission has always regarded Vepco's Surry and North Anna plants as among the most security-conscious in the country, according to a regional NCR spokesman. He said the agency is now rexamining security procedures at both plants and has sent safeguard investigators to both sides.

"It may be that the system was entirely adequate but that someone with the proper authority and access did this," said Ken Clark of the NRC's regional headquarters in Atlanta.

Entry to the fuel storage building is gained by using a "key card" to unlock the door, Vepco said. Each time someone enters or leaves, the date, time, point of entry and number of the card is recorded in a computer.These records are being checked by the FBI.

Surry, Clark noted, has had an unusually high number of construction workers at the site recently because of repair work being done to steam generators for one of its units. But he said they would not normally have access to the fuel storage building.

Vepco's Cochran said the contaminating crystals have been washed off about half of the affected fuel elements. While the FBI investigation continues, he said, Vepco has made "some adjustments" in security assignments for the site to provide "more thorough coverage."

Security arrangements will be a matter for Vepco and the NRC, said agent Ervin. "It's not the FBI's prerogative," he said. "But however tight they may have been before, you can be sure they will will tighten them even more."

All but essential workers were evacuated from the Surry plant last night as the result of an anonymous telephoned bomb threat. A Vepco spokesman said the plant was searched and no bomb found.