Last year the Northern Virginia Regional Park Authority opened a dozen vacation "chalets" overlooking the Potomac River, including one with a hot tub.

Now, at the same Algonkian Regional Park on the Loudoun-Fairfax County border, the park authority has opened a rustic conference center complete with roaring fires in huge stone fireplaces -- in season -- and scenic vistas over the Potomac.

The 500-acre park also contains one of the region's largest swimming pools, boat-launching ramps and "what we are told is the best public golf course in the Washington area," says park authority spokeswoman Dorothy Werner.

At prices of $40 an hour for each of the three large rooms, the new convention center may not be affordable for local civic groups, but already it is being booked by businesses, said Werner. With a large kitchen also available, the center is capable of handling conferences of 12 to 200 people.

The center was created by a just-completed $300,000 remodeling of the large golf club house that the park authority acquired when it bought the property in 1976 from the Potomac Electric Power Co., which used it as a recreation complex for its employes.

Beside building patios and large glass picture windows for the center, the park authority added a 200-car parking lot and a large woodpile. Wood fires are included in the rental.