A state arson unit is investigating a fire that severely damaged last week an Occoquan restaurant operated by the owner of an historic Occoquan mansion that was gutted by an arson last year.

David Huff, an arson investigator with the Virginia State Police, described the fire at Blackbeard's Restaurant as being "of suspicious nature," although no cause has been determined.

The restaurant is owned by Donald L. Sonner, who owns two other restaurants in Occoquan and Rockledge, an 11-room stone mansion on on the western end of the small Prince William County town.

The fire at the seafood restaurant at 302 Mill St. in Occoquan caused extensive damage to the dining room, a lounge, offices and storage space above the dining room, according to Occoquan fire officials. No one was injured in the fire, which was reported at 3:45 a.m. Oct. 19, fire officials said.

Sonner estimated the damage to Blackbeard's at more than $200,000, although Huff estimated the damage at about $100,000.

This is the second time in two years that one of Sonner's properties has been the subject of an arson investigation.

In January 1980, Rockledge was nearly destroyed in a late-night fire that was determined to have resulted from arson. Richard C. Elderth of Woodbridge was convicted on a charge of arson in the case and sentenced to eight years in prison.

That fire caused an estimated $250,000 damage to the house, which was designed in 1758 by William Buckland, the architect who also designed Gunston Hall, George Mason's home in Fairfax County.

Sonner, who had finished a $250,000 renovation just before the fire occurred, says he has not started to rebuild the home because he did not have enough insurance to cover the damage.

The Historic Preservation Society in Occoquan, however, is applying for federal and state grants to purchase and restore the mansion, which is part of an historic district created by the Occoquan Town Council earlier this month.

Besides the fires, Sonner has been a victim of vandalism several times since he began restoring Rockledge in the mid-1970s. Two years ago a goat he kept at Rockledge had its throat cut, and in another incident, the windows were smashed on a truck he owned, Sonner said. Since the Rockledge fire, the remains of the house have been vandalized, he said.

"I think they're all unrelated to one another," Sonner said, adding that he thinks Occoquan is "a sleepy little town" that is experiencing an increase in all types of crime as its population grows.

As he cleaned up from last week's fire at Blackbeard's, Sonner said, "I'm just trying to pick up the pieces and keep going."