HRB-Singer Inc., a division of The Singer Co. Products and Services for Government Group, recently opened its new Maryland operations in Lanham.

The company says the staff at the headquarters, which currently amounts to about 75 employes, is expected to grow to about 200 within the next year, and then increase by 1985 to 500 employes with an annual payroll of $13 million.

The Singer Co. is engaged in the design, development and marketing of aerospace and marine electronic systems for government and industry. The company also manufactures and sells sewing products and consumer durables.

A formal ribbon-cutting ceremony for the new building in Lanham will be held in the spring of this year.

Developments in real estate in the Washington area:

* The Dominion Bank Building at 200 N. Washington St. in Alexandria was recently sold to E.L.M. Marks for $4.5 million. The colonial-style building, which was completed in 1966, contains approximately 60,000 square feet of office space.

* The Barlow Corp. of Chevy Chase will begin development of a 296,000-square-foot building in Gaithersburg. Office space in the $30 million structure, which should be completed in early 1984, is expected to rent for about $20 per square foot.

* Centennial Development Corp. has purchased 30 acres in Reston from the Reston Land Corp., a subsidiary of Mobil Oil. The land, which sold for over $3 million, will be the site for Sunrise Technology Park, a complex of eight industrial buildings designed for occupancy by research and development companies. Construction should be completed by 1982. Space will lease for about $6.50 to $7 per square foot.

* The U.S. Geological Survey will lease 26,000 square feet of office space in the Herndon Parkway Building, located at 1110 Elden St.

* The Hechinger Corp. recently purchased from Beltway Properties 6.5 acres of property adjacent to Security Square Mall in Baltimore. Hechinger's plans to build an 85,000-square-foot retail store and a 20,000-square-foot garden shop on the site.

* Professional Associates of The Psychiatric Institute have leased 9,300 square feet in the Bethesda Office Center at 4520 East-West Highway. The transaction completes leasing of all available space in the center, which is owned by Rozansky & Kay.

* A Large parking lot at 2401 Pennsylvania Ave. NW was sold recently by Tad A. Lindner and others for $2.6 million to Bar H Ranch of Nevada. Lindner is associated with Colonial Parking Inc.

* Long and Foster Realtors recently announced the acquisition of the Columbia-based firm Clark and Associates Realtors. Garnett Y. Clark Jr., former head of Clark and Associates, has been named a vice president in charge of new home sales in Maryland for Long and Foster. The acquisition, which was the first for the company, gives Long and Foster 39 offices. Its sales for 1981 have been reported close to $1 billion.