More than $100 million in sales were made in June by the multioffice Long & Foster Realtor firm that operates throughout the metropolitan area. It was the highest volume in the firm's 12-year history.

Wesley Foster, president, attributed the record volume -- including 1,105 sales of new and existing houses -- to an upturn in buyer confidence and lower mortgage rates. "The market has responded throughout the area and buyer confidence is strong," he added.

The firm's previous highest volume month was recorded in April 1979, when the total exceeded $93 million.

Foster said that the Gaithersburg office had the highest volume in June -- more than $10 million for 120 house sales. The unit sales of the firm leveled off in April at 684 and picked up to 987 in May. Long-Foster has offices from Frederick, Md., to Fredericksburg, Va., and from Crofton, Md., to Marshall, Va.

Earlier, the Washington area office of Ryan Homes reported that it had sold 416 new houses in June. Regional manager Arthur Titus said that Ryan had 259 sales in Northern Virginia, including 85 in Newington Forest, plus more than 100 in Montgomery County. The firm builds mainly moderately priced dwellings at varied locations in a wide-ranging area. Some of its two-bedroom houses are priced under $50,000.