ANITA AND SHELDON Shalit, and Dennis and Carol Frings have much in common, though the Shalits live in the city and the Frings in the country.

Each couple (30s and early 40s) has a young child. Both couples are willing to devote a good portion of their professional salaries -- and a vast amount of time -- to build a custom home, suited to their informal life style. Both have recently moved into new houses designed for them by Glenn Chen Fong of Arlington. The 30-year-old architect not long ago was designing houses and office buildings on family land in Hong Kong.

Not that there's anything oriental about the Shalit and Frings houses. Fong says the major influence in his architectural philosophy is the late Louis Kahn, his professor at the University of Pennsylvania. "He was always talking about light and what it did to spaces."

Light was a prime consideration for both the Shalit and the Frings houses. How to get light into both of them presented different problems, though the answers in both cases were contemporary with no traditional allusions, except for the materials, the brick structure of the Shalit house, the wood siding for the Frings.

The Shalit house is a rowhouse on Capitol Hill, facing east. The Frings house is detached, in the midst of six acres of land in Great Falls, with tall trees shading the house's principal south and west orientation.

In both houses Fong used the trick that works for more and more architects today, in both the city and the country. He reached up to the sky for light.

Not long ago, Fong took us on a tour of the two houses.