With Chairman John F. Herrity the lone dissenter, the Fairfax County Board of Supervisors yesterday approved a $1.6 million sewer system for 169 Fairfax families, more than half of whom are now using outdoor toilets.

Approval of the limites system in the Lincoln-Lewis-Vannoy community, one and a half miles west of Fairfax City, is a victory for Supervisor Marie B. Travesky (R-Springfield) who has been the most outspoken, champion of installin some type of sewage treatment service in the low-income neighborhood.

The sewer system, to be operational in 1979, will permit residents of the community to have bathrooms and kitchens with standard plumbing fixtures. It will require a county contribution of $750,000, the first half of which will be budgeted next year. The balance will come from federal community development block grant funds.

The particular sewer system chosen will move households wastes under pressure through underground plastic pipes to four local treatment plants and then to underground beds where the treated sewage will soak into the soil and provide nutrients for grass and shurbbery growing above.

Kenneth A. Hosto, an environmental scientist for Kamber Engineering, said the pressure system was chosen over four others because it is appropriate for rural, low-density areas and is as efficient as more costly systems. It is designed to handle only "a small flow - only domestic waste from 351 single-family units," he said and so should not encourage uncontrolled development.

But Herrity, who called his sole negative vote a difficult one, said he believes installation of the sewerage system will cause property values, and therefore taxes and rents, to rise, eventually forcing out many of the law-income residents in the homes on Braddock, Popes Head and Calchester roads.

Pointing out that many of the 351 lots in the affected area are owned by people who do not live in the community, Herrity said the "real issue is where will the ultimate benefit lie, with the people who live there or with the people who own the land." Approximately 40 per cent of the 169 families are renters, according to a county report.

Speculators and real estate developers, Herrity feels, will be attracted to the area now that it has a sewage capacity.About 42 per cent of the Lincoln-Lewis-Vannoy neighborhood now is largely vacant or largely undeveloped, according to a county report.

Herrity said he would have preferred to see individual chemical or incinerator-type toilets put into each home. Hosto told the board yesterday that these types of toilets "don't work succesfully" and that "there is a problem with odor."

In support of the sewerage plan, Supervisor Martha V. Pennino (D-Centreville) said the main question is, "should we like to have an incinerator toilet in our homes or have an outhouse? The answer is no.'"

The citizens who live in "this outpost of the county should have the right to enjoy the same kind of way of life as we do," she added.

One limitation on development in the neighborhood is the fact that Lincoln-Lewis-Vannoy has been made a "conservation area" which, according to Martin E. Crahan of the county's Housing and Community Development Agency, "prohibits any rezonings." The area, the third in the county to be designated a "conservation area," is now zoned for one family dwelling unit per acre.