The Coast Guard and the National Transportation Safety Board announced plans yesterday to begin hearings later this week into the Saturday capsizing of a coal-carrying vessel off the Virginia coast.

More than 30 crew members died or were reported missing in the accident.

Preliminary investigations by safety officials and Coast Guard records of ship inspections have provided little evidence so far to indicate why the 605-foot Marine Electric, an American-owned collier carrying 24,800 tons of coal, capsized and later sank about 30 miles east of Chincoteague, Va.

"The indication is the water that came over the ship's bow caused the capsizing," said Ralph E. Johnson, a safety board investigator. "They were pumping, but couldn't keep up with the amount of water." Johnson said, however, that it is not clear why water started pouring over the bow, and he said there is no evidence of any shortcomings in the ship's pumps.

The vessel was examined in December by Coast Guard safety officers, a spokesman said yesterday, and was found sufficiently seaworthy to be granted a two-month delay in its previously scheduled drydocking inspection.

The safety examination turned up three minor deficiencies, all involving the ship's fuel-oil system, said the Coast Guard spokesman, Lt. j.g. Eric Shaw, in Boston. There has been no indication that the fuel-oil system played a role in the accident. The deficiencies included possible corrosion of an oil storage tank wall, possible wearing out of an oil pump's foundation and need to replace a temporarily patched oil pipe.

The ship underwent full inspections in June 1981 and June 1982 and was found to be safe, Shaw said.

There have been uncorroborated reports of defects in the ship. The Wilmington News Journal reported over the weekend that a former fire--man and engineman, Calvin L. Johnson, had described the ship as so trouble-plagued that "she should have been scrapped."

A spokesman for Marine Transport Lines Inc., the New York-based firm whose subsidiaries owned and operated the ship, declined comment yesterday, saying the cause of the incident is under investigation.

The hearings by a five-member Coast Guard and safety board panel were tentatively scheduled to start Wednesday in Norfolk.

In addition, Rep. Brian J. Donnelly (D-Mass.) called yesterday for a congressional investigation of the incident.

The number of crew members still missing was uncertain yesterday. The Coast Guard, after interviewing survivors, reported nine crewmen missing, but the shipping firm said its records indicated that only seven remained to be found. Three crewmen survived and 24 bodies have been recovered.