The joint construction of a 150,000-square foot office center and a 309-room hotel at 1750 Rockville Pike has been topped off.

The $50 million project, known as the Twinbrook Office/Holiday Inn Complex, is adjacent to the Twinbrook Metro stop, which is also under construction. The 6 1/2-acre office/hotel complex is scheduled for completion next summer, prior to the opening of the new Red Line station.

Rozansky and Kay Construction Co. is developing the office facility, a six-story building with more than 12,000 square feet of ground-floor retail space; Mardeck Ltd., which has developed and operated Holiday Inns since 1962, is managing the hotel development. The two brick-and-concrete structures will be joined by a one-story arcade.

Spokesmen for both developers said the extension of subway service to the Rockville station will significantly increase demand for hotel and office space in the area. "The joint venture is meeting both a demand and an opportunity," said Mardeck vice president Malcolm Lingwood.

Donohoe Construction Co. is general contractor for the project.

Other recent developments in commercial real estate in the Washington area:

* Judiciary Square Office Building at 633 G St. NW has been topped off. Occupancy of the eight-story brick structure is scheduled for late this year. Under development by T/I Associates, the building will contain 100,000 square feet per floor, with an additional 55,000 square feet of underground parking and office space. Smith, Segreti & Tepper are the architects; general contractor for the project is Tiber Construction Co.

* Construction of a 123,000-square-foot office building will begin later this year at 9th Street and Maine Avenue SW on the District waterfront. The four-story building, to be owned by NBL Associates Limited Partnership and developed by Demar, Inc., is expected to be ready for occupancy in late 1983.

* A 65,000-square-foot office building at 1411 K St. NW has been sold for about $6.5 million to an investment group headed by Robert Moran and Barry Stern. The property was sold by 1411 K St. Associates Limited Partnership, which purchased the building in 1977.

* The Wire Building, on McPherson Square at 1000 Vermont Ave. NW, will reopen for occupancy late this summer following extensive renovation. The 12-story structure, under redevelopment by owner Theodore J. Georgelas, contains about 6,700 square feet per floor.

* Link Simulations Systems, a division of the Singer Co., has leased 101,000 square feet in Sieling Business Center's Columbia II Building at Dobbin and McGaw Roads in Columbia.

* New York Life Insurance Co. has leased 8,315 square feet in the Barlow Building, 5454 Wisconsin Ave. in Chevy Chase.

* Integrated Micro-Computer Systems (IMS) has purchased an 8,300-square-foot building at 5320 Marinelli Road in Rockville.

* Aztech Electronics, Inc., a distributor of computer components, has leased 6,600 square feet in at 8940-E Rte. 108 in Columbia's Oakland Center. The company relocated from offices in Glen Burnie.

* O'Boyle Tank Lines, a fuel transport company, has leased 6,223 square feet at 2215 East Jefferson St. in Rockville.

* Highway Film Service, Inc., a distributor of motion picture film and publications, has purchased a warehouse and offices totaling 45,000 square feet at 15103-15113 Marlboro Pike in Upper Marlboro. CAPTION: Picture, The $50 million hotel-office complex on a 6 1/2-acre site on Rockville Pike.