An unusual 130-foot waterfall will cascade down a stair-stepped, park-like facade on one of three downtown office buildings to be started in 1980.

Architect Arthur Cotton Moore designed the waterfall wall for a 289,000-square-foot building that will be the headquarters of Consumers United Group at the southeast corner of 13th and L streets NW.

Consumers United Insurance Co., the parent organization that handles group health plans, bought the 27,430-square-foot site for $2.3 million from the Washington Daily News Co. The site has been a parking lot since that newspaper plant was razed about five years ago.

Moore said the 12-story building was designed to provide "an exciting element along 13th Street instead of the usual setback or court," in addition to coordinating with the building's retail and community spaces and also with Franklin Park. More than half of the building will be leased to other tenants.

The John Akridge Co. and Realtor William Morris plan to start another $13 million, 10-story office building at 919 19th St. NW to replace an older building that had been converted from an apartment building to office use. The Brainard Warner Trust owns the site and will be a partner in the new building designed by Weihe, Black, Jeffries, Strassman & Dove. Salus Corp. plans to begin construction in March.

Also, demolition is exprcted to begin soon on the south side of I Street NW, where an 11-story office building designed by Smith, Segretti & Tepper will be built by Wilco Construction co. of Rockville.

Hal Boles of Coldwell Banker, which will handle the leasing at 1722 I St. NW., said the polished granite exterior will be enhanced by a curved notch above the mid-block entrance in the center of the building. The 181,000-square-foot structure will have glass-enclosed retail bays on lower floors, which will be half levels above and below the street grade.

The plans for these three downtown office buildings indicate a continued confidence in new development despite high levels of new construction in recent years. For instance, the Consumers United Group building at 13th and L demonstrates a trend that recognizes future viability for new space in the office leasing market east of 15th Street. This trend is expected to continue through the 1980s.

The other two buildings, on I and 18th streets, will be part of the continuing redevelopment of the downtown area west of 16th Street. Both developers are forecasting leasing schedules in the range of $19 a square foot.

Akridge said the building at 919 18th st. NW will be leased on a basic $15-a-square-foot basis with an initial operating expense factor of $4.50 a square foot being added. "That operating factor will be adjusted annually to keep pace with expected increases in operating and energy costs," he said.