Fairfax County's growth through the rest of the decade will exceed the combined growth of Montgomery and Prince George's counties. But in the next decade home building in Fairfax will slow down, and there will be a dramatic increase in suburban Maryland, especially in Prince George's.

These are some of the conclusions reached in a two-month Fairfax County staff study ordered by the Board of Supervisors in response to a Washington Post article Nov. 14. The story said that Fairfax would lead other area jurisdictions in growth for the foreseeable future, because the county had plentiful sewer capacity and land zoned for homes, in contrast to the Maryland counties.

The report, which was considered by the Fairfax Board of Supervisors at their meeting on Monday, said that in the long run the rate of building in the metropolitan area would balance out. By 1990, Fairfax County will be receiving only its "fair share" - about 26 per cent - of total growth in the metropolitan area, the report said.

In a discussion of the report Monday, the six supervisors present appeared reassured that the staff was indicating that growth would remain at a controllable level in the county, but their remarks were peppered with large doses of skepticism about whether all available methods of accurately forecasting Fairfax's population trends have been exhausted.

Supervisor Alan H. Magazine (Mason) said the report "doesn't make me feel good but I feel better than I did when I read the (Washington Post) article." Magazine said he knew the board was tired of considering land use problems but he feels they must give more attention to this area since "we still have some serious problems to address."

William B. Rucker, a specialist in growth management in the county's Office of Research and Statistics an author of the report, said the expected turnaround on growth was based on population projections compiled by the Metropolitan Washington Council of Governments.

According to those projections, Prince George's growth would jump from an average of 5,700 annually in this decade to 21,600 annually in the next decade. The projections show Fairfax's growth falling from 19,000 annually in this decade to 13,700 annually in the next decade.

According to Rucker's report, the projected surge in Prince George's will happen because of "expected resolution of sewer problems and . . . increased market pressures . . ." These factors, he added, would ease present growth pressures on Fairfax.

The report acknowledges that such long-range population forecasting is "highly susceptible to error due to unforeseeable factors which may affect population growth." For example, population forecasts of the 1950s failed to anticipate the tremendous movement of newcomers to the Washington area.

David W. Sheatsley, a demographer with the Fairfax Office of Research and Statistics, said he was skeptical that Prince George's would absorb all the growth projected for the county. "The figures tend to be political," he said. "I really don't see any reason for a dramatic gain."

Elizabeth B. Davison, a planning coordinator for Prince George's at the Maryland National Capital Park and Planning Commission, noted that the estimates for growth were drawn up before the county adopted a sewer-allocation policy that rations construction of multiple-family dwellings in one major growth area.

The policy, she said, "could have a major effect" in constraining growth in the county, she said.

Other experts have cast doubt on Prince George's achieving its announced intention of emphasizing the construction of single-family houses to attract the high-income residents who have flocked to Fairfax and, to a lesser extent, Montgomery, in recent years.

The Washington Post article said that if Fairfax grows by 30,000 people annually for an extended period of time, the county would be hard-pressed to meet the demand for public services and facilities. The article cited examples of service gaps resulting from current growth.

The Rucker report, however, says the 30,000-annual growth would be only a temporary surge during 1978 and 1979.

During the board discussion, Martha V. Pennino (Centreville) spoke of her "gut feeling" that "we reached the peak of quality of life in Fairfax County five years ago and it's been declining ever since."

Pennino reiterated her desire to see the board set a ceiling on the number of people they would allow into the county and to come to the figure by asking themselves "how many people can this land mass called Fairfax County accommodate from the point of view of esthetics and quality of life?"

The most outspoken critic of the report was supervisor Audrey Moore (Annandale), who questioned using figures supplies by the Metropolitan Washington Council of Governments since "these projections have proven unreliable in the past."

Moore called for a study of projected economic population growth in the county that would be based on broad economic factors because, she said, "builders will build where it's cheapest." She said the economics of Fairfax County that make it less expensive to build there instead of in other metropolitan suburbs would determine more than anything else future growth patterns.