Two sections of thin surface plaster about a square foot each and 1/4-inch thick, fell from the ceiling of the Kennedy Center's Grand Foyer onto its red carpeting yesterday afternoon. But the Kennedy Center is a big place and its management merely moved 3-400 opera and theater goers - and the champagne bars - into adjoining halls and went on with the show.

On arrival last night, the audience for "Porgy and Bess" was directed to enter the Opera House through a side entrance in the Hall of Nations, while the audience for "Absent Friends" was directed to one in the Hall of States.

Plaster falls had occured at 11 a.m. and at 2 p.m., when seepage from Tuesday's dramatic rainstorm worked its way through to the foyer ceiling.

The re-routing through doors normally used for the disabled, with the expected result of curtain delays, was because of "supersafety precautions" made even though the plaster was too light to hurt anyone, according to the Center's director of operations, Thomas Kendrick. Kendrick made the decision with the advice of National Park service engineers.

Such leaks have occured before and were patched at a cost of $10,000 in time for Inauguration activites. The leaks, located in the marble roof terrace above the foyer, will not be

The Center has had water problems since is construction. The Center [WORD ILLEGIBLE] resealed last May, held up during Tuesday's storm.

The roof terrace and plaza drive [WORD ILLEGIBLE] extensive repairs however, and [WORD ILLEGIBLE] million was appropriated by Congress for that purpose last month.

Construction drawings for those repairs are expected to be completed in September, after which bids will be solicited.

The Grand Foyer will be closed to tourists this morning until the rest of the Tuesday rain is given a chance to make its way through the ceiling. Then a decision will be made about using the foyer - which can hold 10,000 people - or part s of its or tours and intermissions. No plans to curtail performances have been announced.

The areas of damaged plaster are just outside he main steps to the Opera House, and a few feet further south.Regular checks will be made, but no purely decoratice repairs are scheduled [WORD ILLEGIBLE] the major work is done on the terrace. "You reach a limit as to how many times you want to spend $10,000," said Kendrick.

It has been estimated that it will cost $500,000 to repair the terrace, and another $90,000 to fix the ceiling.