When author William Peter Blatty moves into the house he is buying on Georgetown's Prospect Street he will return to the scene of his own and the devil's work, so to speak.

It was on this bluff along the Potomac that much of the action took place in his best-selling novel, "The Exorcist," and it was here that film footage was shot for the subsequent movie.

Realtor Beau Bogan says he is selling his Prospect Street house to Batty for around a half-million. The house's glass-enclosed rear addition -- with a 40-foot, spiral staircase that is one of the tallest in the city -- overlooks the Potomac from a perch above Key Bridge and is a spectacular sight from below.

That stretch of Prospect Street near 36th Street is one of extremely individualistic homes. The ground there was filled in some 40 years ago and the homes have been owned or rented by Supreme Court justices, Senators, society figures, builders and others.

When Bogan purchased the house seven years ago, it was not much more than a burned-out shell; the previous owner had died in the fire that nearly destroyed it.

Brogan later added the glass addition with the aid of architect John Ruffner.

The arrival of Blatty, who wrote so chillingly of exorcism, heightens interest in this block of Georgetown, with its homes of historic and architectural interest. The home he will occupy is a few yards from the steep steps down to M Street where a central character in "The Exorcist" met his death.

Brogan and Blatty go to settlement Jan. 14. The Prospect Street property is the latest in a string of homes the Washington realtor has lived in and sold to such folk as California's new Republican Sen. S. I. Hayakawa, and Reps. Richard Krueger (D-Tex.) and Pierre du Pont IV (R-Del.), newly elected governor of his state.

A property veteran in Georgetown, Bogan also made a name for himself over the last two decades on Capitol Hill, where he has been active in restoration and remodeling.

Bogan plans to move back to Capitol Hill -- to the 700 block of 6th Street SE --

"About five years ago I sold the most desirable house on that block for $50,-000 -- today I bought the least desirable for $80,000," he said.

Blatty is reportedly seeking firmer footing in the Washington area to research another book. His ties to California apparently remain uncut, however. It was also recently reported that he recently bought the Hollywood home of actor Kirk Douglas.

Carolyn Hughes is a freelance writer.