British Aerospace and Rolls-Royce have moved into a $3.8 million North American headquarters and Warehouse facility near Dulles International Airport in one of the largest foreign investments in the Washington area.

The two companies are sharing an 84,000-square-foot facility on six acres that currently stores $21 million worth of engines and spare parts for servicing about 1,000 aircraft in North America that were built by British Aerospace companies or are powered by Rolls-Royce engines, or both.

British Aerospace Inc. has moved commercial, engineeridng, sales, purchasing and public relations offices to the Dulles plant and closed its Arlington offices.

Accordidng to R.J. Gladwell, executive vice president and general manager for British Aerospace whose firm has been selling successive generations of aircraft in North America for 24 years.

"To succeed, a foreign manufacturer must make a substantial and visidble investment in the U.S. marketplace both to ensure a high level of spaces, engineering, training and operations support geared to American standards . . . and also to demonstrate his long-term commitment to the support of his aircraft on this continent."

Gladwell forecast 1978 volume from his operations here of about $80 million. Currently, he said, British Aerospace has 600 customers in the U.S. market, including 30 airlines and 230 companies that own corporate planes.

John MacDonald, First Secretary (Commercial) at Britain's Embassy here was among participate in the Board of Trade international program yesterday. He said about 50 British concerns now have operations in the greater Washington area.