Fairfax City's heavily traveled downtown streets will become increasingly clogged in the next five years unless traffic is rerouted around the city, according to a comprehensive plan approved by the planning commission this week.

For a city already 90 percent developed, one of the biggest problems looming in the 1980s is controlling traffic.

"In every direction around Fairfax City, there are major development changes planned, and this affects our traffic," said city planning director Richard Massell. "Because we are so built up, we tend to be sensitive to changes next door or down the road."

To detour traffic west of the city, the comprehensive plan suggests that city officials push for Fairfax County to extend Shirley Gate Road between Lee Highway and Waples Mill Road and support the Springfield Bypass. For an eastern bypass, the plan recommends early completion of an $11 million project to widen and realign Pickett Road and connect it through to Route 50.

By 1990, according to Metropolitan Council of Governments projections, 197,000 persons will live within a four-mile radius of Fairfax City--an increase of almost 62 percent over the 1977 population. In addition, COG projects that 59,800 persons will work in this area by 1990, a 91 percent increase over 1976 employment figures.

With those statistics in mind, city planners have spent years drafting a comprehensive plan for preserving Fairfax City's "residential character." The plan, for example, calls for city officials to take steps to control the proliferation of fast-food restaurants and amusement arcades along commercial avenues.

Within the next three months, the City Council is expected to approve the state-mandated plan, which capsulizes the city's expected land use and development problems for the next five years.

"Our city has its fair share of commercial development," Massell said. "What we need in the years ahead is residential development. We need enough school children to keep the schools going."

Since 1970, the number of Fairfax City children enrolled in schools has plummeted from 5,991 to 3,310 this year, the comprehensive plan reports. During that same time, the number of households in the city increased from 6,574 to 7,050, but the number of persons per household decreased by one.

To attract more families, the plan suggests that the city subsidize housing for lower-income families and protect undeveloped, residentially zoned land. Of the 460 undeveloped acres in Fairfax City, 75 percent is zoned residential. If developed to its maximum potential, the land could accommodate 1,200 additional dwellings for about 3,600 persons.