The Pennsylvania Avenue Development Corp. (PADC) has commissioned advant-garde American sculptor Richard Serra to design a "major work of art" to be placed at the western terminus of the avenue between 13th and 15th Streets.

Once designated to become a four-block "National Square," the White House end of the avenue is now to feature two plazas, along with a rearrangement of roadways and sidewalks to make the area more pleasant and less confusing.

The announcement of Serra's appointment was made at his dealer's, the Leo Castelli gallery in New York's SoHo. The final choice of the artist was made by PADC, with the assistance of the National Endowment for the Arts, which acted as consultants.

Serra will be part of a team of architects, planners, engineers and landscape architects, also named yesterday, who are to attack "the problems of vista and pedestrian-vehicular conflict that have turned the western sector of Pennsylvania Avenue into a noisy, traffic-clogged intersection."

One of the proposed new plazas is to be located between the Washington and Willard Hotels and the Commerce Department Building. It is to be designed by a team headed by Philadelphia architects Venturi and Rauch.

The second plaza, to be located in front of the District Building, will be designed by a team headed by landscape architects M. Paul Friedberg and Partners.

The panel which suggested Serra named five artists from which PADC made its choice. The other four are said to have included Claes Oldenburg, Richard Morris and Mark di Suvero. The NEA panel included art historians and curators from all parts of the country.

The design teams met for the first time last week to brainstorm the project. They will continue to meet to coordinate their design, which is expected this summer. Construction will begin within a year, according to Pennsylvania Avenue Development Corp.

No dollar figure for Serra's sculpture has been set, but it will be less than 1 per cent of the projected construction cost of $14 million.

Educated at the University of California and at Yale, Richard Serra, 39, has a reputation among younger artists and critics as one of the most creative of the sculptors who emerged in the late '60s. Like many advanced American artists, his work seems better known in Europe than in his own country.

Europe especially acclaimed Serra's huge abstract steel sculpture "Terminus," which served as center-piece for the avant-garde "Documenta 6" art exhibition at Kassel last summer. The piece consisted of four 12-meter-high (about 13 yards) trapezoidal slabs of unpolished steel, leaning against one another like a house of cards.

Serra said he does not know yet what form his Pennsylvania Avenue sculpture will take. "It will probably be something one can walk into, through and around," he said. "But unlike the piece at "Documenta 6," it will focus not upon itself, but upon the site and the great vista down Pennsylvania Avenue."