The Army wants to station more soldiers at Joint Base Lewis-McChord to build up a helicopter brigade, but not as many as an earlier plan suggested.

The base stands to gain about half the 2,700 soldiers it would have added had the Army made Lewis- McChord its first choice for a new combat aviation brigade.

Instead, an environmental study released Friday shows the Army favors creating the brigade at Fort Carson, Colo., sending the full allocation of soldiers and 112 helicopters to that base beginning in October 2012.

Lewis-McChord, once a contender for the new brigade, would get another combat aviation brigade, but it would be fashioned partly out of units already stationed at the base. It would gain 1,400 soldiers and 44 helicopters under the Army’s preferred plan.

A decision on how to stand up the new helicopter units is expected after March 7.

The Army wants to add aviation resources because they’re in high demand in Iraq and Afghanistan. Soldiers in the Army’s existing aviation brigades typically have less downtime between deployments than other service members.

Commanders at the bases want the aviation brigades because they enhance training opportunities for other units that work with helicopters when they deploy.

Colorado’s congressional delegation crowed Friday about Fort Carson taking the lead in gaining a full, new brigade. Washington leaders said the Army proposal shows the Defense Department values Lewis-McChord.

“It’s growth no matter what scenario we look at,” said George Behan, a spokesman for Rep. Norm Dicks, D-Belfair.

The Army population at Lewis-McChord has grown steadily over the past decade, rising to 31,350 this year up from 23,000 as recently as 2007.

That quick expansion strained the South Sound’s highways and cities. The new environmental study reflects the concerns, citing the likelihood that adding 2,700 soldiers and a full component of helicopters to the base would have “significant” effects on noise, traffic, biological resources and housing.

Environmental effects in those categories were considered “less than significant” at Fort Carson.

Fleshing out an aviation brigade from Lewis-McChord’s current resources still would have environmental effects, and the report outlines some steps the Army plans to take to limit its footprint, such as:

 • Conducting helicopter training exercises at times that minimize their noise effects on surrounding areas.

 • Installing a traffic signal and traffic island at DuPont-Steilacoom Road and East Drive.

 • Requiring helicopters to fly at least 2,000 feet in the air when passing over Nisqually Wildlife Refuge.

 • Collaborating with state, local and federal agencies to address traffic congestion on Interstate 5.

The Washington Department of Transportation wrote a letter to the Army requesting more attention to traffic issues, particularly at entrances to Lewis-McChord along Interstate 5. The Army acknowledged likely traffic tie-ups in its 623-page report and left open the door to more transportation projects.

“These potential effects on traffic on road leading to JBLM are significant and warrant further investigation and identification of long-term mitigation actions,” the report says.

Lakewood Senior Planner Dan Penrose also wrote a letter to the Army expressing his city’s concerns about potential effects on services such as roads and schools. On Friday, he said the Army proposal recognizes that “Joint Base Lewis-McChord is clearly a growth spot for the Army as they’ve continued to grow over the past seven years or so. It bodes well for the region that the Army continues to place more units here.

“It’s just nice to see that the military is continuing to invest in our area,” he said.