General Motors Corp. plans to build a new Washington regional headquarters off Interstate-270 in the City of Rockville, informed sources said yesterday.

The nation's largest automobile manufacturer has signed an option for about five acres of land on Piccard Drive, near Valle's Steak House restaurant and the Joseph R. Harris Co. headquarters, southeast of the I-270 intersection with Shady Grove Road.

Argonaut, a real estate division of GM, plans to close a deal on the land purchase in the near future - possibly next week. Apparently, GM is working with local government officials in developing an Industrial Revenue Bond offering to help finance the development.

GM has been searching for a regional headquarters building here during the past 18 months. The company's real estate officials reviewed sites in McLean, Va., Prince George's County and various locations in Montgomery County before settling on the Rockville parcel.

A Washington-Baltimore regional office consolidation will take place after the new building is constructed. Of about 340 area-based GM employes, more than 200 would be moved to the 1-270 complex, already zoned for the type of medium-sized office center being planned by the auto manufacturer.

One source said GM plans an initial structure with between 60,000 and 80,000 square feet.

Officials of GM here and in Detroit declined to comment on their office building plans but said they may have "an announcement" next week. "Nothing has been signed," beyond the option, said one GM representative.

Montgomery County spokesmen either declined to comment or did not return a reporter's telephone calls.

The attraction of GM to Rockville and Montgomery County represents a significant achievement for economic development officials there although the auto manufacturer's plans for the Washington area do not match those of Mobil Oil Corp., in aggressive Fairfax Country. Mobil has started construction of a domestic division headquarters in Northern Virginia to house more than 1,000 workers, initially.

Informed sources said the GM move reflects a decision to combine at one location offices now scattered around the Capital Beltway - the regional Buick division in McLean, Cadillac in Gaithersburg, Chevrolet in Chevy Chase, Pontiac in Rockville and Oldsmobile in Columbia.

Other GM offices that may be located in the new building include GMC Truck & Coach, now in Silver Spring; AC-Delco, in Gaithersburg; and General Motors Acceptance Corp., an auto loan firm, with offices in Alexandria and Bethesda.

Apparently, GM patent offices in Arlington and a training center in Fairfax would not be involved in the consolidation.

GM earlier tried to buy a five-acre parcel from Martin Marietta Corp., near Montgomery Mall. But Martin was seeking more money for the land than GM wanted to pay and there was a dispute over a proposed highway overpass across 1-270 that GM did not want for fear traffic would spoil the park-like setting.

The new GM building in Rockville is expected to generate substantial property tax revenues to Montgomery County and result in the addition of some jobs to the county's employment base. Reportedly, another unidentified company is planning a much larger expansion in the county.

One of the wealthiest counties in the nation. Montgomery has been seeking new business development because there has been a dramatic decline in the portion of its overall tax base represented by the commercial-industrial sector. From a high point of 20 percent in 1970-1971, the commercial-industrial portion has dropped to less than 14 percent, placing an increased burden on homeowners.