The Nuclear Regulatory Commission will direct all operating nuclear reactors in Maryland and Virginia to shut down for at least a week to inspect for cracks in a nozzle leading to the steam generator.

The closings are part of a nationwide effort to inspect all 33 reactors built by Westinghouse Electric Corporation and Combustion Engineering Company, after six of the 13 Westinghouse reactors already inspected were found to have the cracks and require repairs.

Commission spokesman Frank Ingram said the order will require the owners of the reactors to inspect within 90 days for the cracks which, if undetected, could cause "a buildup in heat and pressure in the reactor itself," Ingram said.

Ingram said the inspections would take a week, and, any repairs required would probably take another week.

Spokesmen for the two utility companies with nuclear reactors in the area said they were unaware of the forthcoming order, and could not gauge what effect it would have.

Charles Franklin of the Baltimore Gas & Electric Company, owners of Calvert Cliffs in Maryland, which services 800,000 customers, said the directive would probably not hamper operations at Maryland's nuclear plant, because the first of the two reactors shut down for maintenance and refueling since April will not reopen until mid-July, and the second is already scheduled to close down for a few months in September. Franklin said the inspections for the cracks could easily be added to the routine maintenance.

Although Franklin said he could not calculate the effect of the shutdown on an individual consumer's utility bill, he said his company must pay an additional $550,000 each day that the reactor is closed and replacement oil must be bought.

August Wallmeyer of the Virginia Electric and Power Company said only one of the four existing reactors is presently operating, and that the closing of that one reactor, North Anna Unit One in Louisa County, could have a serious effect if the other reactors could not open within the next 90 days, making difficult the search for an energy replacement for Vepco's 1.2 million Virginia customers.

Vepco has asked permission of the NRC to reopen Surry Unit One, closed in March by the NRC to test its ability to withstand earthquakes, and to open a new reactor, North Anna Unit Two.

A spokesman for Westinghouse builders of 25 of the 33 pressurized water reactors in the nation, said that the problem is the responsibility of the architect-engineers of the systems, but that the company is responding to numerous requests for assistance from the utility companies affected.