Construction has begun on Space Center Tysons, a $25 million, 875,000-square-foot building located across Rte. 123 from Tysons Corner Shopping Center on Westpark Drive.

The Space Center will wrap around an existing structure, the 13-year-old Honeywell building. Connecting the two buildings will be an atrium for restaurants and shops.

Space Center Tysons, whose address is 7900 Westpark Dr., is scheduled for completion in December 1986.

Space Center Tysons is being developed by Space Center Tysons Inc. and was designed by Clark Tribble Harris and Li, Architects. The building was constructed by Omni Construction Inc.

Other recent developments in commercial realty in the Washington metropolitan area:

* Financial Services Group and Coldwell Banker have leased space in Courthouse Center, a 255,000-square-foot office building located at 1953 Gallows Rd. in Tysons Corner. Financial Services Group, a financial planning firm, has leased 21,282 square feet for $3 million. Coldwell Banker has leased 17,866 square feet for $1.25 million.

* Equitec Institutional Real Estate Fund has purchased the Cresent Plaza, a 132,207-square-foot office building at 7700 Leesburg Pike, Falls Church, from Summit Hialeah Properties, according to the agent, Coldwell Banker.

* KEF Electronics of America Inc., which distributes loudspeakers, has leased 11,049 square feet at Dulles South Two, located in the Sullyfield Business Park in Fairfax.

* Suburban Bank has leased 4,275 square feet at 1577 Spring Hill Rd. in Vienna from SASC Corp.

* Casde Corp., a government computer consultant, leased 11,723 square feet at 1150 South Washington St., Alexandria, from Huntington Development Corp.

* Developers Mortgage Corp. and Oxford Development Corp. have leased 9,829 square feet and 12,000 square feet, respectively, at 7315 Wisconsin Ave. in Bethesda from Bethesda Air Rights.

* Washington Business School has leased 9,541 square feet at 8233 Old Courthouse Rd. in Vienna.

* Network Strategies Inc., a contracting firm, has signed a lease for about 10,000 square feet at 8617 Westwood Center Dr., Vienna.

* Fairfax Radiological Consultants Inc. has signed a $1 million lease for 6,067 square feet at 3299 Woodburn Rd., Annandale.

* Beboul, MacMurray, Hewitt, Maynard and Kristal, a law firm, has signed a lease for 3,009 square feet at 1111 19th St. NW.