McDonnell Douglas will build a Santa Ana complex.

The first phase of the complex, a 300,000-square-foot, $23-million office and manufacturing facility, will house about 850 workers from existing units of the company’s computer systems operation. McDonnell Douglas, which purchased 52.5 acres in Santa Ana last year, said it ultimately will construct a 1.8-million-square foot, $150-million office, research and manufacturing complex for its information systems group, which now is housed in 14 separate facilities in Orange County. The first phase is scheduled to be completed in mid-1988, the company said.