When a goal-oriented home builder under 40 becomes tired and listless and sleeps through the weekends, he seeks medical help. That's what David H. Miller did more than five years ago. He saw a lot of medical men before a "brilliant diagnostician" at Johns Hopkins located a pituatary tumor and a "gifted neurosurgeon" removed it.

Since then Miller has regained his old zip and now, at 43, heads the Miller and Smith firm that expects to complete 120 single-family houses and town houses this month at a break-neck pace.

Meanwhile, Miller is also giving a lot of his time and energy as president of the Northern Virginia Builders Association. He considers an adequate water supply for future growth as the NVBA's major challenge.

A native of Webster Groves, Mo., and a mechanical engineering graduate of Purdue University (1954), Milgot his start in residential construction with an uncle. After college he served three years in the Navy an the engineering officer of an amphibious vessel and then went to Harvard Business School. There he met Gordon Smith and Otis (Skip) Coston. They worked for other builders here until 1964, when they formed Miller & Smith. Coston still has a financial interest but now works with the group developing Burke Center.

Miller handles the production side of the business and Smith takes care of financing and administration. They are now building in a number of moderate-priced subdivisions, having abandoned more expensive, contemporary lines of houses, such as Drumaldry in Bethesda, several years ago. Now they do traditional styling and hew to affordable price ranges. A few years ago the firm experimented with a modular production operation in Gainesville, Va., but abandoned it.

Miller and his wife live in Bethesda but the firm's office is in McLean. They have three children in high school or college. Since regaining his health, Miller is working harder and enjoying it more. "The most satisfying aspect is seeing what you produce and having the pleasure of providing houses that people can afford and enjoy," he said.