During the last six years, the Washington metropolitan area gained more than 145 million square feet of commercial building space -- an amount equal to 22 Pentagons -- with 43 percent of it in the vicinity of existing or planned Metrorail stations, according to a new study.

Half of all the commercial development in the region took place in Northern Virginia, with Fairfax County alone adding almost 43 million square feet of commercial space, or 30 percent of the total, according to the study released yesterday by the Metropolitan Washington Council of Governments.

The study is further evidence of the region's rapid transformation from a center of government bureaucracy to a boomtown of service industries, defense contractors and high-tech firms. Commercial space includes several categories: offices, stores, government buildings, hotels and other types of nonresidential construction.

During the study period, developers built 67 million square feet of office space in the region from 1980 through 1986, three times the amount of office space in all of New Orleans, according to the Office Network, a Houston-based organization of independent real estate brokers.

According to the study, developers built almost 62 million square feet of commercial space within seven-tenths of a mile of 78 existing and planned Metro stations.

"That's not too much of a surprise," said Jim Eichberg, president of Smithy Braedon, a major commercial real estate firm. "The development community saw years ago where those Metro stops were going to go and put a lot of faith, and rightly so, in public transportation."

The Metro Center station at 12th and G streets NW led all other stations with more than 5 million square feet of new space, 1.5 million of it in new hotels. The next three stations were McPherson Square, Crystal City and West Falls Church.

Of the $8.4 billion worth of commercial construction projects in the region during the period covered by the study, Northern Virginia attracted the greatest share. Developers in Northern Virginia built 72 million square feet of commercial space, compared with a combined total of 73 million for the District and the Maryland suburbs.

Northern Virginia accounted for 36 million square feet of office space, 4 million more than the District and Maryland combined.

In Fairfax, commercial development was concentrated on main roads intersecting with the Capital Beltway, as well as areas out I-95 to the south, and along the Dulles access and toll roads and the I-66 corridor to the west.

"Fairfax is a really good market," said Jay Langford, COG's director of planning. "It's got airports on either side of it, it's got proximity to Washington, it's got two wonderful new freeways, I-66 and the Dulles Toll Road. That gives it a real competitive advantage."

Both Montgomery and Prince George's counties also showed considerable growth. Montgomery added 24 million square feet of commercial space, most of it near Metro stations on the I-270 corridor, according to the study. The study also noted that a "second growth corridor" is taking root along Rte. 29.

In Prince George's, developers built 17 million square feet of commercial space during the study period, mostly in the northern end of the county near Laurel.

By comparison, development in Loudoun and Prince William counties was modest. Loudoun recorded 3.3 million square feet of new commercial space, while Prince William added 5.5 million square feet, according to the study.

Eichberg, who expressed confidence that the boom is a long way from over, said the region's office vacancy rate of 12 percent compares favorably with other East Coast cities. The vacancy rate in the District is 10 percent.

But he added, "It's not without its problems. Obviously, transportation is the issue now and for the future."

Langford sounded another cautionary note. "This is becoming something of an artificial economy here because of the amount of foreign investment," he said. "We're receiving investment that is disproportionate to the size of the area's economy."

In other action, the COG board voted 11 to 1 in favor of a resolution by D.C. Council Chairman David A. Clarke supporting the District's efforts to keep the Washington Redskins in the city. Redskins owner Jack Kent Cooke has said that Robert F. Kennedy Stadium is too small and has threatened to move the team to the suburbs if the city does not build a larger arena.

Hilda Pemberton, chairman of the Prince George's County Council, cast the only vote against the resolution, saying that the council wished to "keep its options open."

Her vote appeared to signal a rift with Prince George's County Executive Parris Glendening. On Tuesday, Glendening issued a statement in support of a plan by D.C. Mayor Marion Barry and Fairfax County Board Chairman John F. Herrity to unite the region behind the effort to build a new stadium in the District.