The roof over Metro's new, unopened $19 million Grosvenor station has large cracks in it. It is being propped up by huge timbers while engineers decide whether it is falling down and what to do about it if it is. The Washington Post has learned.

The station, located on the east side of Rockville Pike just outside the Beltway, is not scheduled to open until early 1983, so there's time to fix it.

"We now regard this as a design deficiency," said John S. Egbert, Metro's assistant general manager for design and construction. That means that the designer, not the contractor, is being held responsbile for the work.

The design work on the station was done by the York, Pa., firm of Buchart-Horn Inc. for $951,000. John B. Jung, president of the firm, said yesterday that "I am not aware that it is [Metro's] view that is is a design problem. All I'am aware of is that there is some cracking . . . We do plan to act responsibly on this."

The station was built from Buchart-Horn's designs by Expressway Construction. It is an outdoor station with a large parking lot.The roof is suspended over the platform areas. Panels of plastic arranged in pyramid-like fashion extend down the center of the station to provide light.

Grosvenor is one of the stations on the line that will someday run from the operating Dupont Circle station to Shady Grove. Under Metro's present schedule, the line will be extended from Dupont Circle to Van Ness Center in Washington in early 191, then the rest of the way to Shady Grove in 1983.

Another unopened station of similar appearance. Addison Road on the Prince George's County end of the Blue Line, does not have similar problems, Egbert said.

The problems at the Grosvenor station were first noticed in May by engineers and inspectors from the Bechtel Corp., Metro's supervising contractor, according to Egbert.

"Bechtel noticed some cracks," Egbert said, and we began to watch it and check the design. In August, we noticed there had been some additional movement so we put in some temporary work [the timbers] to hold it."

Egbert said the Metro is now studying ways to fix the ceiling "without having to destroy part of it."

One technique under consideration, Egbert said, is called "post-tension, Egbert said, is called "post-tensioning," Reinforcing steel in the ceiling would be placed under tension and drawn more tightly into the support points.

Metro had a similar but different problem last year at the Cheverly station, on the section of the Orange Line due to open Nov. 20. In that case, reinforcing steel was found to have been improperly placed during the construction.