The Washington area's more than 3,000 military reservists, who have been meeting in cast-off government buildings around the nation's capital, now gather at one of the country's newest and largest military reserve centers, built on a former runway at Bolling Air Force Base.

The $9.6 million building, to be dedicated Saturday, opened last fall as the once-a-month training ground for nearly 100 reserve units from the Army, Navy, Marine Corps, D.C. National Guard and Coast Guard. They include helicopter, submarine, military police, medical and combat units, as well as the National Guard's 257th Army Band, which will perform at the dedication.

"They can't believe that this is for the reserves.... they're used to old, dilapidated, deteriorated buildings," because most of the reservists are sailors, says Navy Capt. Donald Stull, who is in command at the two-story brick-and-glass center.

Combining the military branches and their scattered reserve untils is an effort by the Department of Defense to reduce training costs. There is no official estimate of the savings to be made at the new building, although Stull says it will cost less to heat and light than the half-dozen buildings previously used. And he proudly notes that the new center cost $1.2 million less than DOD estimated and Congress provided.

According to a military spokesman, the center is -- at least for the moment -- the last major building planned for the 920-acre Air Force base, which closed its runways in 1962 and was declared surplus in 1965. The District government once hoped to build a mini-city for 25,000 persons on the site, but the late Rep. Mendel Rivers (D-S.C.), chairman of the House Armed Services Committee, pushed through a bill prohibiting civilian use until 1975 because he opposed use of Bolling "for the social concoctions of some idiots around Washington."

The Defense Department, in turn, was blocked in its efforts to build a "Little Pentagon" at Bolling, but various military construction projects were approved. By 1975, more than $40 million in new military buildings and housing for more than 1,000 military families was being constructed.

Three final projects are under-way at Bolling: completion of a $1 million underground heating distribution system for the base, a $1-million energy-saving computer control to automatically operate heat and air conditioning in base buildings and a small automotive repair building. There are 2,170 military and civilian employes on the base and about 3.900 military dependents. The Air Force Band and Honor Guard and numerous Pentagon support units for the Air Force are stationed at the base.

About 800 of the "weekend warriors" are D.C. National Guard members who were crowded into the D.C Armory or World War I and II buildings at Camp Simms, a former Army rifle range just off Suitland Park-way and Alabama Avenue SE. The guard now has only 25 of the original 190 acres at Camp Simms. Much of the land has been transferred to the District, the Department of the Interior (for Suitland Parkway), Greater Southeast Community Hospital and the General Services Administration.

Most of the other 1,500 Guard members here are still stationed at the Armory, with some at Fort Belvoir. However, virtually all other military reservists around Washington are now going to bolling for their weekend meetings and will leave from there this summer for their annual two weeks of active duty.

The 1,600 Naval reservists and 500 Marines now at Bolling used to meet in a trun-of-the-century brick building at the Washington Navy Yard, and some Naval units met in a WORLD War I boat-building office at the National Park Service's Jones Point Park in Alexandria.

The smallest reserve group is the Coast Guard, with 180 reservists who formerly met in the 60-year-old Ford factory on Alexandria's waterfront, adjacent to Jones Point.

While the new reserve center has many classrooms and an indoor dirlling area larger than a football field, most of the weekend meetings are "hands on" sessions, says Stull. At those sessions, reservists work outdoors on equipment or work in the military specialty they're trained to do. The D.C. National Guard military police units, for instance, often do police work at Fort Belvoir and other nearby forts.And Coast Guard units regularly inspect small boats for safety equipment or supervise safe handling of dangerous cargo at such places as the liquid natural gas facility at Cove Point, Md.