Roger L. Stevens, the magisterial head of the Kennedy Center, sat down at a picnic table on the sea porch of the Eugene O'Neill Theater Center last week and spoke. He was dressed in shorts and open-necked shirt - not his customary apparel - and the mood was informal as he chatted with participants in the National Critics Institute.

Among this remarks:

"It was pure stupidity on the part of the Metro planners" when they failed to build a subway station at the Kennedy Center. Stevens said he wants to institute shuttle bus service between the Center and the subway stop at George Washington University when the Metro "develops into a real subway" or whenever there's enough public demand for the service.

The Friends of the Kennedy Center "has not done the job for us financially and we're trying to beef it up." Asked later for details, Stevens said that he and FOKC boss Lily Polk Guest would provide some in "a couple of months."

"If I had my uppers, I'd do all new plays all the time, except when some great star wanted to do a revival." Asked what happened to the six new plays commissioned by the Kennedy Center and Xerox for the Bicenternial, Stevens said, "We commissioned the wrong playwrights." The Center plans to stage only one of the plays - "A Place on the Magdalena Flats" by Preston Jones.

"If there is going to be a national theater, the Kennedy Center would be the place for it." New York, where so many theaters already exist but where the city's primary institutional theater, at Lincoln Center, closed for an indefinite period, is not the place, said Stevens. "And until we get some good writers, I don't know how we're going to do it [start a national theater]."

There are more good new plays floating around this year - about 10 - than there have been for some time, Stevens said. Asked if some of them, or some of the 12 new plays staged by the O'Neill Center's National Playwrights Conference during the past month, might fit the Kennedy Center's new upstairs theater, Stevens said maybe. But he added that the new 500-seat theater would be a fine home for new foreign plays and chamber music concerts too. If all goes as planned, construction on the new theater will begin Nov. 1, aiming for a June 1 opening.