SURRY, Va., Oct. 12 -- Two men on trial for damaging fuel rods at the Virginia Electric and Power Co. nuclear plant here won a major victory today when the presiding judge dismissed four of five charges against them.

Circuit Court Judge Ligon L. Jones' ruling means the defendants, William E. Kuykendall, 26, and James A. Merrill Jr., 24, who each faced up to 51 years in jail if convicted on all five counts, now face a maximum sentence of 10 years each.

The judge let stand one felony charge that the men deliberately damaged Vepco property, but dropped a felony conspiracy charge and a misdemeanor charge concerning the same alleged crime, saying they were "repetitious."

The judge also threw out other felony charges that the men had illegally broken into the plant's fuel building. The judge ruled that the men, who were employed as reactor operator trainees, were authorized to enter the building.

The defendants and their attorneys cited a judge's gag order in refusing to comment on today's ruling, but all were clearly elated. Merrill and Kuykendall hugged their wives and their lawyers, Richard Ben-veniste of Washington and Maurice Nessen of New York, who volunteered their services in the case.

The two defendants have admitted pouring caustic soda over 62 spare nuclear fuel rod assemblies at the plant last April, causing damage Vepco has estimated at more than $800,000. They have contended they acted to draw attention to health and safety hazards at the plant.

The judge's ruling came at the close of testimony by prosecution witnesses, including three FBI agents who read sworn statements that the two defendants gave them last June admitting they had damaged the fuel rods.

In the statements, the men described how they located a drum of caustic soda, pumped it into a five-gallon bucket, and carried it to a fuel building where they proceeded to uncover the fuel rod assemblies and pour the corrosive substance on them.

They said they were interrupted once by a plant security guard, who apparently thought they were doing maintenance in the building, and that several other Vepco employes observed them coming and going from the fuel building but did not question them.

Kuykendall's statement said the damage was done in part as a warning to Vepco that its security was lax. He said he could easily have used a crane in the fuel building to lift highly radioactive spent fuel rods out of a storage pool and caused a major release of potentially deadly radiation.

"I attacked the most vulnerable area in a manner that indicated the potential for disaster," Kuykendall's statement said.

Kuykendall said he had time to commit the damage because of sloppy work practices at the plant. "I had had no job for more than a week because my supervisor didn't know I worked for him," the statement said.

Vepco spokesmen have said the company will not comment on any of the defendants' allegations concerning the plant until the trial is over.