The Defense Department's plan to consolidate the country's military bases would lead to slight increases in the Washington region's traffic and pollution and a minor decrease in mass transit ridership, according to a new analysis.

The Metropolitan Washington Council of Governments and researchers at George Mason University also found that the influx of workers that would be generated by the plan would require an additional 8,500 housing units, mostly in the fast-growing suburbs.

The council's board of directors yesterday approved a resolution urging the Base Realignment and Closure Commission, the nine-member panel reviewing the Pentagon's blueprint for closures, to consider the effect it could have on the area's traffic, housing and economy.

The board joined the growing number of critics of the Defense Department's plan to vacate 4 million square feet of office space in the close-in Northern Virginia suburbs that don't meet security standards imposed after the Sept. 11, 2001, attacks. That could mean the relocation of 23,000 defense workers.

The Pentagon also wants to close the Walter Reed Army Medical Center in the District.

The region's suburbs would fare much better under the plan, which will need approval from President Bush and Congress. Anne Arundel County's Fort Meade would gain 5,300 jobs, Fort Belvoir in Fairfax could grow by as many as 18,000 and the Marine Corps base in Quantico would add 3,000 workers.

By 2020, when the full effects of the changes would be felt, mass transit trips in the region would drop 0.52 percent, while vehicle trips would grow 0.34 percent, according to the 33-page report. The region's poor air quality would worsen with the increased traffic, the report said.

"That is clearly going in the wrong direction," said David Robertson, executive director of the council of governments. "We want to see more transit use, not less. . . . We want to see air pollution declining, not going up."

While the percentages are low, the increases in traffic would be concentrated at specific points, such as the highways leading to Fort Belvoir and Fort Meade, said Ron Kirby, the council's director of transportation.

Prince William County would need to add 3,000 of the 8,500 new housing units projected under the plan in the next 15 years, the most of any jurisdiction in the region, according to the report. Fairfax County would need an additional 2,000, and Montgomery County would require 1,000.

The region would initially lose 11,000 jobs, but it would add almost 19,000 workers by 2020, the report said.