The white crystalline substance dumped into stored fuel elements at the Surry nuclear power plant in Southeast Virginia was identified yesterday as sodium hydroxide, also known as caustic soda, stored in large drums at the site and used to clean water-purifying equipment, according to a Virginia Electric and Powder Co. spokesman.

Identification of the substance heightened speculation that what Vepco calls "attempted willful damage" to fuel supplies, discovered Monday, was the work of someone employed at the station.

"It appears to be an inside job," said Vepco spokesman Doug Cochran, who cautioned that the FBI has yet to draw any conclusions from its investigation into the incident.

Vepco, meanwhile, has cut back on the number of employees allowed access to the fuel storage area where 62 fuel elements were temporarily contaminated with the corrosive alkaline substance. Each fuel element consists of 225 12-foot-long zirconium rods that contain uranium fuel pellets.

"We've made some changes in security procedures to provide greater coverage in certain areas, and we've reduced the number of people from 125 to about 20 who normally have access to the fuel storage building," Cochran said.

Those who are still allowed into the area are mainly members of the cleanup crew working on the fuel assemblage, which Vepco said appears to be undamaged by the chemical.

The crew and most other employes at the plant were temporarily evaculated from the site Wednesday night after the Surry County sheriff's office received a bomb threat from an anonymous caller. He said a bomb had been set to explode in the plant, but when no bomb was found workers were allowed to return.

"We've had bomb threats at both plants before and at our offices," said Cochran, referring to Vepco's second station at North Anna in Louisa County.

Cochran said such threats seemed to coincide with publicity about the power station or actions by Vepco, such as utility rate increases.