A 30-year-old window washer who dangled precariously from a rope 12 stories above Pennsylvania Avenue NW was pulled to safety yesterday by the joint efforts of an off-duty policeman and three other men. The dramatic rescue was witnessed by hundreds of office workers and noon-hour strollers.

Kenneth Pryor, 30, and Alonzo Washington, both employes of a maintenance firm, were lowering their scaffold from the 12th to the 11th floor of the Presidential Building, at 1115 Pennsylvania Ave. NW, when a support broke, D.C. police reported.

As the scaffold plummeted to the sidewalk, police said, Washington pulled himself to safety, but Pryor danged from a rope to which his safety belt was attached. As the rope swung, Pryor struck the side of the building, apparently hitting his head, authorities said.

Washington tried to pull his co-worker to safety, but could not manage it by himself. Bernard Taylor, 27, an off-duty policeman who saw from the sidewalk what had happened, hurried to the top of the building, where he was joined in his rescue effort by special policeman J. R. Williams and two other men, Adrian Thompson and Anthony Fernandez.

Together, they hauled Pryor to safety. He was taken to Georgetown University Hospital, where he was treated and released.