The latest arrival on Pennsylvania Avenue - Skidmore, Owings & Merrill's design for the Heurich office building-is not Great Architecture, thank God!

It is, in my view, good architecture precisely because it cheerfully joins the chorus rather than trying to be a prima donna. It also, without apparent effort, solves a number of tricky design problems.

We thus have one more indication that "the main street for both the city and the nation" will indeed "be lively, friendly and inviting as well as dignified and impressive," rather than a frustrated pomposity.

The quoted prescription was written 18 years ago by Sen. Patrick Daniel Moynihan (D-N.Y.), who was assistant secretary of Labor in the Kennedy administration at the time. Passed in by then-Labor Secretary Arthur Goldberg, it became a presidential order.

The frustrated pomposity - a protracted and enthusiastic effort which, it appeared, was out of tune with the changing mood of the country-has been discussed often in this and other columns.

What is new is that, due in part to the intelligent energy of W. Anderson Barnes, the executive director of the Pennsylvania Avenue Development Corp., the future vitality of the Avenue seems now assured.

We have cut the dramatics, remembered to respect history and got down to the difficult business at hand. That business, in the words of corporation Chairman Joseph B. Danzansky, is "to encourage the liveliest possible mixture of uses in the area, including restaurants, theaters, art galleries, and speciality shops that naturally attract large numbers of users and stimulate street activity both during the day and at night."

The latest evidence of cutting dramatics happened on a new stage, the space between 13th and 14th Streets or, roughly, between the District Building and the National Theater. At present this space in the middle of Pennslyvania Avenue is messed up by dribbles of roadways running every which way and islands in between.

Some years ago Charles Atherton, the secretary of the Fine Arts Commission, drew up a brilliantly simple new traffic pattern which creates two squares - a Western Plaza and an Eastern Plaza. It is now under construction.

Architect Robert Venturi (Venturi & Rauch) was commissioned to design the Western Plaza. He created an intricate, richly adorned platform from which two huge pylons were to rise. The pylons suggested a triumphal arch which was not a triumphal arch but only a metaphorical landmark. I thought they were great.

But I also thought that Venturi had Burdened his splendid idea with too much Disneyland gook - stars and stripes and marble models of the White House and God knows whatelse.

This burden of kitsch, I am afraid, toppled the pylons. But the intricate platform will be built with a marble inlay L'Enfant Plan on the floor, a pool, benches, planting and a great deal of literature writ in marble - historic quotations selected by Florence Ladd, a native Washingtonian who now teaches urban studies at MIT.

Landscape architect M. Paul Friedberg (with a battalion of associates and consultants) designed a nifty little park for the Eastern Plaza. The trees will shelter a memorial to Gen. John Joseph Pershing, which has also been scaled down from a more grandiose design.

Evidence of the new historic respect is manifest in the resurrection of the Willard Hotel and the almost whimsical manner in which it is to be enlarged. Yes, architects Hardy Holzman Pfeiffer's design is a bit theatrical. But in contrast to the architectural stunts that seem the rage in the New York fashion magazines, the addition is but a gracious cusrtsy to grand dame Willard.

Another of the landmarks saved on the Avenue is the old Evening Star building on 11th Street. And that is where the ingenuity of the Heurich Building design comes in. It is to be built between 13th and 12th Street on property formerly owned by Christian Heurich the beer brewer.

Under the discarded Pennsylvania Avenue plan the Star was to be torn down and the Avenue was to be widened. In keeping with this widening idea, the new Presidential Building on 12th Street was set back some 50 feet. So now the lovely old Star Building sticks out rather awkwardly.

But the Heurich Building, to the west, across 12th Street, comes to the rescue. For some three-quarters of its total length along the avenue it is also set back in line with the Presidential Building. Then on an elegant angle, returns to the regular building line. This device creates a pleasant open space which the designers and owner of the Heurich hope to fill at least in part with an outdoor cafe and other amentities.

Like the new buildings in the next block west, between 13th and 14th Streets, the Heurich will contain two ground floor levels of shops and restaurants as well as an iterior concourse, skylit and terraced inner court and all. John Portman and his lofty Hyatt-Regency courts really started something.

The $18-million office building, developed by Cabot, Cabot & Forbes of Boston, a nationally prominent real estate firm, will aslo give us a two-story arcade along the avenue as well as an arcade diagonally through the building towards the Metro Center subway stop at 12th Street.

Among the ingenious design solutions is the basic grid on which the building is constructed.It runs parallel to the 19.5 degree angle with which Pennsylvania Avenue cuts through the street grid and it has 30-foot by 40-foot bays. This creates unusually large column-free interior spaces and a triangular interior court.

The building is faced with pink granite. On the avenue facade the granite is rough cut, matte and dignified. Along E Street, in keeping with the somewhat more flashy character granite is polished. The glass is to be copper tinted.

With this design, (which shows again that the Washington office of Skid-more, Owings & Merrill is more sensitive to its surroundings than the New York office which have us the Hirshhorn museum) the liveliness of the western part of Pennsylvania Avenue seems assured.

What happens on the eastern end, depends largely on whether the General Services Administration will permit the restored Old Post Office to become the tourist attraction it ought to be.

GSA is used to building stodgy federal offices for stodgy bureaucrats. It is not used to its new freedom, granted by recent legislation, to make public buildings public. It therefore ought to turn the marvelous interior court and the lower floors of the Post Office over to the kind of developer who made Fanheuil Hall Market or Ghirardelli Square such imaginative attractions.

The avenue d*eserves nothing less, to say nothing of the 15 million tourists who crowd Washington's Mall every year. CAPTION: Picture, Artist's rendering of the Heurich Building