More than $1.3 billion in federal construction and development projects -- about $220 million in Montgomery and Prince George's counties-- has been recommended for the Washington area during the next six years by the National Capital Planning Commission (NCPC).

The major suburban Maryland project is the long-proposed $140 million Beltsville headquarters and laboratories for the Food and Drug Administration. If Congress allocates the funds to begin construction during the next fiscal year, about 1,625 federal employes would be moved to the new headquarters from various downtown Washington buildings over the five or six years it would take to complete the complex.

NCPC's annual proposals by 16 federal departments and agencies does not include the proposed Silver Spring headquarters for the Nuclear Regulatory Commission and its 3,000 employes, a controversial project now before Congress.

The federal government initially planned to lease a large office building for the NRC but now plans to buy land and build its own building in downtown Silver Spring, within walking distance of the Metro subway station. That switch came because Congress has imposed a moratorium on the increasingly expensive practice of leasing office space for federal agencies.

The other major federal projects proposed in Montgomery County are a $23 million modernization of the Bethersda Naval Medical Center, an $18 million U.S. Postal Service maintenance facility, $4 million in improvements to the Army's Forest Glen section of Walter Reed Army Medical Center and a $2.1 million expansion of research facilities at the Army's Harry Diamond Laboratories in Hillandale on the Montgomery-Prince George's border.

The Navy Medical Center improvements call for interior and exterior renvovation of eight buildings, landscaping and new security entrances to the hospital complex. Improvements at the Amry's Forest Glen section call for a new commissary warehouse, a new access road and a $2.5 million community services building.

In Prince George's besides the proposed $140 million FDA headquarters in Beltsville, sums recommended for other major federal projects include $10.5 million for expansion of Andrews Air Force Base, $2.6 million to stabilize the walls of historic Fort Washington $10 million for a regional museum storage complex in Suitland for White. House and National Park Service collections, and $4.7 million for a new Amtrak station at New Carrolton.

The Andrews AFB improvements include $2.2 million for construction of a Ready Crew Alert center, $2.1 million for an auto maintenance shop, $1.1 million for a data processing facility and $5 million for 400 units of dormitory housing for enlisted personnel. Most of the improvement will replace 20-year-old, deteriorating buildings.

At Fort Washington, the National Park Service proposes to spend $2.6 million to stabilize the soil around the historic fort overlooking Mount Vernon. Considered the nation's finest post-Revolutionary War fort, most of Fort Washington's historic buildings have been boarded up for decades and the fort itself has had little restoration.

The proposed new $10 million Park Service storage warehouse, on a site near the Suitland Federal Center, would replace various storage sheds that now house extensive historic and archeological collections from the White House and Washington area.

Not all the 144 construction projects proposed by federal agencies and approved by NCPC will be built, at least not in the near future, because Congress usually approves funds for only 50 to 75 percent of the requested projects.

Last year, for example, Congress approved annual funds for only 33 of 52 proposed federal projects here (63 percent). Most of this year's 19 unfunded projects are included in NCPC's new 1981-1986 capital-improvements program, although many could be deferred again.