Virginia state arson investigators yesterday refused to release any information concerning the cause of a fire that destroyed a historic mansion near the Occoquan Gorge in Prince William County.

Rockledge, the 11-room, three-story mansion designed in 1758 by colonial architect William Buckland, was ravaged by fire late Thursday night. The blaze left only "the stone frame" standing according to Lt. Roger Cordani of the Prince William fire department.

Arson investigators refused yesterday to make any dollar estimate of damage to the mansion, once described in a federal survey as beng "worth of most careful preservation for the benefit of future generations."

The mansion, which was last assessed at $130,000 in 1974, is owned by Donald L. Sonner of Occoquan. Sonner said yesterday he has invested more than $250,000 in restoring the mansion since he bought it in 1971. He said he plans to rebuild the landmark, which he said is insured.

More than 60 firefighters worked into the early morning yesterday trying to control the blaze, which was reported about 11 p.m. Thursday. Two women firefighters suffered heat exhaustion and were briefly hospitalized.

Rockledge architect Buckland also designed the famed George Mason's Gunston Hall in Fairfax County and Hammond Harwood House in Annapolis.