With Mayor Marion Barry playing an outspoken role, directors of the Pennsylvania Avenue Development Corp. voted decisively yesterday to kill plans for erecting two slab-like pylons in a new plaza being built near 14th Street NW.

The 85-foot-high pylons, which would have framed the view of the U.S. Treasury as seen from the direction of the Capitol, had sparked a sometimes-bitter national debate among architects and city planners.

After Barry spoke against the proposal, saying it would detract from the nearby District Building -- Washington's city hall -- as well as other landmarks, the board decided by a lopsided voice vote to drop the idea.

It was the third time the board of the government-sponsored corporation dealt with the idea, having agreed earlier not to build the pylons as part of the original construction program for the plaza but to leave a decision for the future.

To facilitate possible eventual construction, the board was asked yesterday whether to install foundations for the pylons in the new plaza at a cost of $175,000.

Preliminary work is uder way for the plaza, which will extend from 13th Street to 14th Street, blocking off the existing diagonal stretch of Pennsylvania Avenue. Westbound traffic will be diverted onto what is now E Street, in front of the existing National Theater, and eastbound traffic will be diverted in front of the District Building.

Robert Venturi, the Philadelphia architect who is designing the plaza, and J. Carter Brown, director of the National Gallery of Art and chairman of the U.S. Commission of Fine Arts, both argued for the pylons. The fine arts unit reviews public architecture in Washington.

Inscribed with words from the Constitution, the pylons would "send shivers down the spines of... those who visit here," Brown said, and would enhance the city's L'Enfant master plan.

The proposal to kill the pylons was made by Yvonne Perry, who represents the U.S. secretary of Housing and Urban Development on the board. She was joined by Nathaniel A. Owings, a prominent retired architect and vice chairman of the corporation, and by Barry.

By law, the mayor is a board member, and yesterday's meeting was the first attended by Barry since taking office. He said he plans to attend the four-times-a-year meetings as often as other duties permit. Former mayor Walter E. Washington rarely attended, sending a planning official in his place.

On another matter, the board officially changed the Pennsylvania Avenue development plan to permit an angled front on an office building planned by Cabot, Cabot & Forbes of Boston on the north side of the avenue between 12th and 13th streets.