Featuring a 25-foot-high, skylighted landscaped plaza, a relatively small, nine-story office building is expected to be started this summer at 1140 19th St. NW.

Developer Robert N. Wolpe said yesterday that the GMR Ltd. design of the 70,000-square foot structure will provide office views for all suites above the third floor. Floor-to-ceiling tinted thermpane glass will be used on the exterior of the concrete structure.

Planned for a 10.463-square-foot site that has been a parking lot, the new structure will be fitted between two small existing buildings on the west side of 19th Street. Wolpe said that the irregular design, broad in back and narrow in front, evolved from a desire to avoid the usual pillbox design."

He said the three-elevator building will have a squash court and possible health club-type facility in the rear of the third and fourth floors. Most of the floor area will be office space, but 15,000 square feet of retail use is planned for lower levels. Wolpe's own firm, at 1732 I St. N.W. will handle leasing. Rent are expected to average $12.50 a square foot.

A young developer who has been rehabilitating some downtown properties Wolpe marks his first new downtown venture with this building.