The stairs are over to the left. The house Blatty wrote about does not actually exist. It’s just a garden there in reality. For the movie they added a false wing to the nearest house (the one you see here), but even then it was still a distance to the steps.
If you click on the link, you will see a bird’s eye view of the house and when you click on the link below the pic, it will take you to a virtual map in which you can zoom in and zoom out to see a better view of the house and the stairs can be seen too from the map. here’s the link:
True. If you click the link, you read: “Description: House at 3600 Prospect in Georgetown which was used (with alterations) for exterior shots in the 1974 movie, ‘The Exorcist’.”
I still don’t understand why the former owner wanted her plain picked fence back after WB spent all the money creating the wrought-iron and brick fence. Go figure.