About 16 gallons of a corrosive acid leaked yesterday from a small hole in a railroad tank car in the Potomac Yard of the Richmond, Fredericksburg & Potomac Railroad Co. in Alexandria, fire and company officials said.

The cause of the leak, which was repaired in about an hour, has not been determined, said Fred Wilson of the Alexandria Fire Department. "There was a small hole, about the size of a dime, midway along the tanker," he said.

At no time was the surrounding community endangered, according to fire officials.

RF&P officials said there were no injuries or major interruptions of train traffic in the rest of the yard.

The tanker, which was stationary when the leak was discovered by RF&P employes yesterday morning, was carrying 17,000 gallons of concentrated hydrofluosilicic acid, a chemical commonly used in the fluoridation of drinking water, according to James Wenzke of the fire department. The chemical spilled onto the track surrounding the tanker, according to RF&P officials.

Hydrofluosilicic acid causes burns when it comes in contact with skin and eyes and can be harmful if inhaled.

"It's not a bad chemical," said Wilson. "It wasn't as bad as we thought."

Hazardous-chemical specialists from the fire department neutralized the acid with lime and water.