American Multi-Cinema Inc. has announced plans to develop the largest multi-screen cinema in the Washington area: a 10-theater complex in Dale City, Va.

The Kansas City, Mo.-based firm, already one of the area's largest theater developers, said it has signed a lease for 36,000 square feet in the 1-million-square-foot Washington Outlet Mall, located at the intersection of Smoketown and Gideon roads near I-95. Western Development Co., which is developing the mall, expects to finish construction in about one year.

AMC currently operates three, six-screen complexes in the Washington area -- the Skyline 6 at Bailey's Crossroads, the Carroll 6 in New Carrollton, and the Academy 6 in Greenbelt -- and is constructing a fourth, eight-screen complex adjacent to its Greenbelt location. One of the originators of the "multiplex" cinema concept in 1963, AMC operates 156 theaters nationally, more than three-quarters of which have six screens or more.

Other recent developments in commercial realty in the Washington area:

* Shimadzu Scientific Instruments Inc., a Japanese manufacturer, has announced plans to expand its Howard County operations.

According to company officials, Shimadzu will triple the size of its Columbia plant to 60,000 square feet and will double employment there to about 70 employes.

The company expects to begin construction in June on the $1.6 million extension of its existing facility, located on a 10-acre site in the Rivers Corporate Park. The building will be used for assembly operations and light manufacturing.

* Marriott Corp. has begun construction on a hotel at the intersection of Route 50 and the Beltway in the Metro East Complex in Prince George's County. The 152-room hotel, which will employ 50 people, is scheduled to open in the fall.

* The Shapiro Cos. said that construction is under way at the 26-acre Green Tec Business Campus, a 300,000-square-foot complex located just east of the Goddard Space Flight Center in Prince George's County. The first of the five structures -- a one-story, 67,000-square-foot building -- is scheduled to open in the spring.

* Urbco Inc., the real estate subsidiary of Connecticut Mutual Life Insurance Co., has begun construction on Watkins Park Plaza. The $8.5 million shopping mall is scheduled to open this fall.

* Suburban Bank has opened its 82nd branch office -- and its third in Columbia, Md. -- at the Oakland Ridge Industrial Center.

* Glen Construction Co. has been selected to construct the first phase of Tycon Towers, the three-building, 17-story office complex designed by New York architects Philip Johnson and John Burgee for Tysons Corner. According to the Gaithersburg firm, the project is expected to be completed in the fall of 1986.