A California developer and former Rouse Co. Executive who has worked on rebuilding the Watts section by D.C. Mayor Marion Barry Jr. as director of the city's Office of Business and Economic Development.

Lawrence P. Schumake Jr., who takes over the District's top business promotion agency starting today, has been vice president for land management since 1978 with Economic Resources Corp. of Los Angeles, where he worked on development of an industrial park and shopping center in Watts, the site of bitter riots in 1964.

Barry, who introduced the new department head at a District Building news conference yesterday, said Schumake "comes to this position with a strong background in business development . . . . His talents combine management experience, professional excellence and community involvement, the very qualities we have been seeking."

The mayor also described activities of the agency as "critical to the future of the District . . . a sound and productive business development program is the key to our plans for continued revitalization and growth to our city."

Organized in 1977 to provide assistance for business development in the District, the office has been operating with funding from federal economic development grants. To date, Congress has refused to approve D.C. government budget decisions to fund the agency's activities, which the city administration has supported as neccessary to halt an outflow of business from D.C. as well as to attract new employers.

Schumake will succeed Knox Banner, a veteran business-development official in Washington who retired from the city post last year.

The 41-year-old developer has worked for more than a decade in urban economic and business programs. He was director of land development for the Black Economic Union of Kansas City, where he planned projects adjacent to that city's central business district.

Although Schumake and Barry didn't make known specific plans for city development yesterday, they both emplasized business retention, expansion of the city's tax base and helping to stabilize neighborhoods that are adjacent to office construction. Barry said the agency will focus on providing opportunities for minority businesses as well as providing jobs for unemployed youths.