MANY OTHER parts of the country might welcome plans for major development by the military, but the neighborhoods of Greater Washington are not exactly giddy at the prospect. This was evident last week when Army officials announced a $2 billion development plan for Fort Belvoir, which would bring an additional 35,000 people to live or work there in the next 15 years. Meanwhile, the Navy would like to consolidate 20,000 military employees who work in leased space in Arlington and Alexandria into one large complex on one of several sites, some already federally owned.

The Army has its land for growth in two areas. One would be the now mostly vacant Engineer Proving Ground between Rolling Road and Interstate 95 near Springfield Mall. This would become a $1.5 billion "public-private partnership" with a builder constructing office space for Army use in exchange for permission to develop the rest of the site. This development would accommodate 10,000 federal employees, 10,000 civilian workers and 10,000 residents. The second expansion would be at the main base along Route 1, with housing, recreation, offices and stores.

What Uncle Sam does with federal property is for Congress and the executive agencies to decide. But local officials necessarily worry about the impact on traffic, the economy, education facilities and the environment. Fairfax County Supervisor Gerald Hyland, whose district includes most of Fort Belvoir, cites a 1986 report by an Army consultant claiming that transportation improvements could cost $150 million. He says these and other such costs should be paid by the federal government. He's right. The head of military base development in this area, Col. Robert R. Hardiman, promises that the Army will pay for off-site transportation and other improvements required by the base's growth.

Fine, but is all this growth necessary? Army officials say the plan would save $43 million in annual costs of private leases. That is a sound policy if it is phased in with an eye to the local market, but hardly the whole answer. Nor is there justification anymore, now that military pay has been raised, for military money and land to go into stores and other establishments that compete unfairly with local commercial establishments. So far in the Fort Belvoir project, officials on all sides are talking about cooperation, negotiations and careful measurement of the economic impacts. That kind of joint approach to growth plans is critical.