Despite an already evident slight downturn in new residential construction, the total realty outlook for 1979 is seen as excellent by a senior officer of a major U.S. real estate firm.

Robert W. Draine, a senior vice president of Los Angeles-based Coldwell Banker, conceded here yesterday that currently high mortgage rates and exceptionally high land costs are areas of concern to the real estate industry in terms of future development. But he insisted the total outlook for industrial and commercial real estate is strong and that the Slowdown in new residential construction will be slight - "not anything like 1975."

Draine, who appeared at a Coldwell Banker presentation-reception for nearly 300 area business leaders at the Madison Hotel, said his firm enjoyed its best year ever in the fiscal year ending in June. "And 1979 looks even better," he added. He said the firm's relatively new Washington office did $150 million in volume in the recent fiscal year.

James O'Brien, head of Coldwell's office here, presented an overview of area commercial and industrial realty markets. He said Washington's dependence on federal government is lessening as federally stimulated areas of private business continue to expand here.