Stocks of major Washington area corporations, as measured by Johnston, Lemon & Co. Inc.'s index of 30 securities, rose 19.1 percent in 1981 while other broad market indicators declined. Of the 30 stocks, 18 were higher--many in the double-digit range.

The Dow Jones average of 30 industrial issues on the New York Stock Exchange fell 9.2 percent, the American Stock Exchange index declined 8.1 percent, Standard & Poor's 400-stock index was down 11.2 percent and the National Association of Securities Dealers composite index for over-the-counter stocks was off 3.2 percent.

The biggest percentage gainer of the 30 area stocks was Government Employees Life Insurance Co., up 96 percent after London-based Legal & General Group offered to acquire the firm at $30.75 a share--ending a squabble between minority owners and what has been the majority owner, Geico Corp.

Geico did well itself. The big insurance holding company rose 88 percent over the year. Other substantial gains were those of Communications Satellite Corp., which is diversifying rapidly into domestic communications and technology; Dart Drug; Financial General Bankshares; First Virginia Banks; Washington Gas Light Co., and Woodward & Lothrop Inc.

Big losers included Fairchild Industries, a Montgomery County aerospace firm that is spending heavily on development of new aircraft, down 60 percent; Martin Marietta Corp.; Federal National Mortgage Association, and USAir Inc.

One new stock has been added to the Johnston, Lemon index--Pargas Inc., a Waldorf-based distributor of propane and owner of coal mines. Pargas replaced Garfinckel, Brooks Brothers, Miller & Rhoads, a retail firm acquired by Allied Stores Corp. of New York.