The areas around Fairfax Drive and Glebe Road in Arlington and East-West Highway and Wisconsin Avenue in Montgomery Country are the two most environmentally sound locations to add federal office space in the next decade, according to a General Services Administration environmental impact statement.

But don't hold your breath waiting for hordes of new federal workers: budget and program cuts and reductions-in-force have left the government shrinking rather than looking for ways to expand.

Before the reductions began, GSA wanted to get ahead of the game and gather environmental information that could be used in expansion plans through the end of the decade. The environmental assessment, along with lease or construction costs and specific program requirements, are the three prime components that GSA uses in planning expansions.

Although the report says the sites have "a high probability for future consideration for federal office space location," the GSA's plans for the next five years currently have two primary thrusts here:

* Construction: GSA is seeking congressional approval for three new federal office buildings--a general purpose building on the Federal Triangle, across 14th Street NW from the Commerce Building; a new Nuclear Regulatory Commission headquarters in Silver Spring, and a new Bureau of Labor Statistics headquarters adjacent to the Labor Department building at 3rd and Constitution Avenue NW.

* Leased Space: GSA Administrator Gerald Carmen says he wants to tighten up on wasted space by compressing the smaller federal workforce into about 20 percent less space within the next five years.

In the impact statement, seven environmental factors were studied at 20 major metropolitan employment centers. "If costs are comparable, and if the space is available, these are prime sites for expansion," says Jerry R. Shipplett, chief of the GSA's National Capital Region facilities planning and environmental branch.

Shipplett said the GSA will use the impact statement as a guide to which negative environmental consequences associated with federal leasing or construction need to be mitigated. The factors reviewed included physical constraints, impacts on historic properties, aesthetics, air quality, noise levels, transportation, impact on existing urban support systems and on the area's socio-economic character.

Only the 70 acres in Bethesda around East-West Highway and Wisconsin Avenue and the 60 acres in the Ballston corridor of Arlington gained more positive marks than negative marks on those critieria.

The socio-economic advantages of adding federal employes to all areas studied was deemed to be "positive," according to the report. Transportation problems presented the most severe environmental constraint, offering a "significant negative impact" at 19 of the 20 areas studied. The only "slightly negative" mark was given to the Ballston corridor because of good access roads and the Metro.

But market factors confound the study, said James G. Whitlock, assistant commissioner of GSA for space management.

"We're confined by the market," Whitlock says, explaining that in the recent attempt to find a new home for the Federal Communications Commission, bids were received for only three sites, and only one--the Hoffman Building in Alexandria-- met the needs. But it was in an area that the impact statement says poses the most environmental constraints.

The draft of the impact statement drew criticism from federal and local officials who complained about the overall GSA space acquisition policy.

For example, James O. Gibson, assistant D.C. administrator for planning and development, challenged the tone of the document, citing the 1978 National Urban Policy that "gives priority to center city and economically depressed areas in the location and relocation of federal activities to help stimulate revitalization." A Prince George's County official said that over the past six years the county has "lost, rather than gained federal jobs" while other jurisdictions were gaining substantially.

Kenneth V. Duncan, chief administrative officer of Prince George's County, noted two major employment centers moved out in the the past several years: the Naval Oceanographic Office to Bay St. Louis, La., and the federal computer center from Prince George's Plaza to Springfield.

"Our office space tenant survey indicates no federal occupancies at all in any of the county's recently completed buildings," Duncan said.

GSA's Whitlock said "they'd sure have a better chance if some of the companies owning the office space submitted bids. Maybe they just don't have the space needed."

Whitlock said that Prince George's County has more space along its share of the Capitol Beltway undeveloped than any of the other jurisdictions, a factor that should help the area "down the road." CAPTION: Picture, Rozansky and Kay's $48 million office complex, "Montrose Metro Park," will go up near Rockville's Twinbrook Metro station.