The Old Post Office, that monumental rockpile on Pennsylvania Avenue, has attracted disasters as though its tower were a magnet. During the dedication ceremonies in 1399, a provincial postmaster fell down the Postmaster General's personal elevator shaft. Killed, of course. The Pendulum on the Great Clock once fell as well. According to the story, it caused no harm because it landed in a bureaucrat's "In" basket.

The building's greatest disaster is also its great triumph, the glass-roofed cortile, or courtyard. The interior court was an effort to provide the poor working office staff, who might not stand high enough in the table of management to rate an outside window, with a little sun and light. Of course, it fried the workers in summer and froze them in winter. Eventually, somebody said "to hell with it" and blacked out the glass. The interior them became a vast black hole, strongly resembling that abyss Luke and Skywalker the Princess swung across in "Star Wars."

A first look at the working or study model for the current remodeling of the Old Post Office makes you feel as though the disaster demon may be on its way to being exorcised by (to use a Victorian phrase proper to the building) the angel of light. The skylight is to become a vast solar collector with finned louvers that are also to act as rotating shunshades. (The original architects of the building, Willoughy J. Edbrooke et al, has the wisdom to put the tower on the north side, the only side not to need louvers, so from the floor of the cortile, the view of the tower will always be unobstructed.) The tower itself, complete with a John Portman-style glass elevator, is expected to be leased out to a commercial company which will operate it as a sightseeing tower.

The Arthur Cotton Moore architectual design for the remodeling of the building is intended. Moore says, to make the cortile "knock your socks off."

The cortile floor will be cut away to show the great stone foundation of the clocktower. On the opposing, or south side, a series of terraced balconies with a fine restaurant on the principal floor, are to go down to ground-floor shops and a cafe. Moore likes to think the ground staircase and the balconies will be used as seats to view morality plays like "Everyman" or Shakespeare performed on the tower steps. A Romeo balcony, helpfully, is already in place in the tower. Such settings have made "castle plays" popular in Europe.

Moore's plan envisions 50,000 square feel of shops and services to the public, with 142,000) square fee of federal offices above on floors 2 through 9. Circling the cortile. Moore thinks the shops should have a sort of "theme" connection with the offices. The National Endownments are already scheduled for the fifth floor, where the eleborate ceremonial offices of the Postmaster General once were. So Moore hopes for art galleries and bookshops in the public spaces. The luxury restaurant is expected to be a drawing card.

Anyway, the model (just completed by Tom Sez. Gary Martinez and Shalom Baranes of Arthur Cotton Moore Associates) now under study in Moore's office, really give the first three-dimensional explanation of Moore's grand plan for the hoary old building. Looking at the model, you can feel at last that the remodeling just might succeed in doing what it's designed to do: serve as a bridge between government workers, tourists from the Mall and townsfolk.

Unlike most government office buildings (and many private ones in this bomb-scare day) where you practically need an armed escort to get in, the Old Office Building is actually designed to invite the public in. Not only that, but it is to be open on Saturdays and Sundays and late at night to give a little life to the otherwise dismal downtown night scene. Moore, and his wife and associate Patricia, are great ones to bike around town on the weekend, and they see the Old Post Office as a splendid destination.

The Moore plan channels the mixed use of the building (a bold innovation for government buildings) so bureaucrats, sightseers and shoppers wont' fail all over each other. The workers primarily will use the Pennsylvania Avenue entrance.

On the Mall or south side, where the old loading docks used to be, the plan is for the public to come in through a spledid curving sculpture courtyard, half circled by an arcade. The court is to serve as an outdoor cafe as well. The nice, arched windows will be lengthened to make tall, skinny entrances. Inside, a part of the first floor is to be cut away in a semicircle for drama, and to lead the people from upper floors down to the shops.

The 12th- and 11th-Street entrances also are planned for the public. The 12th-Street entrance is to be little disturbed. But a new 11th-Street entrance, made by lengthening windows and installing curving steps and a ramp for the handicapped, is to be added to give immediate entrance to the ground floor for shoppers. On Pennsylvania Avenue, people will step down into an entry court from the street and then up curving steps through the great arches. Inside, information booths (security stations in disguise) and glass partitions are planned to separate office wokers from the public.

Arthur Cotton Moore (in a joint venture with McGaughy, Marshall and McMillan of Norfolk, Stewart Daniel Hoban of Washington and Associated Space Design of Atlanta) this summer won the General Services Administration competition for an architect to design the remodeling of the historic structure. In Moore's office, Robert Hammel is projected team leader, and David Cox the senior associate.

Work on the remodeling is expected to begin next summer with completion hoped for in 1980 or 1981. The job has high priorty at GSA, thanks to the new administrator, Jay Solomon. As a matter of fact, Don't Tear It Down, Washington's preservation conscience, was overwhelmed the other night while hearing a report on Moore's design plans for the new building, to notice that a high percentage of the audience was made up of GSA officials. In years past, GSA has spent much time hiding from Don't Tear It Downers. The preservation organization was instrumental in saving the Old Post Office from demolition. And, in return, the project was responsible for the organization of Don't.

A brilliant new 1,000-room hotel - office building incorporating the present National Press Building site, to be designed and developed by Atlanta architect John Portman, is under negotiation nearby on the corner of 14th, 13th and F Streets and Pennsylvania Avenue NW. The Willard Hotel would be restored as a luxury hotel, according to present plans. The Pennsylvania Avenue Development Corp. is already planting rows of trees. So it looks as if at long last, the Capital City might, after 200 years, get around to filking in the space between the Capital and the White House with something other than its traditional traffic jams and porno shops.

Pennsylvania Avenue might even be grand enough for a President to walk down.