Up to 1.7 million new residents are expected to flood the D.C. region within the next three decades, an updated analysis by local governments shows, but politicians and transit advocates are at odds about whether the area is prepared for the spike that could lead to even more gridlock on roadways.

The draft forecast from the Metropolitan Washington Council of Governments calls for the area's population to climb to 6.9 million by 2040, about 131,000 residents more than the group previously estimated.

If the projections come to fruition, it would mean that the region would have grown by nearly one-third between 2010 and 2040.

"We see the strongest growth in the region's suburbs," said Rosalynn Hughey, a D.C. planning official who helped prepare the forecast. "But we also see growth in the District."

Northern Virginia is expected to power much of the expansion, with the population of Fairfax County jumping by 288,000, the most of any jurisdiction in the region.

Where they will live by 2040
Central jurisdictions (D.C., Alexandria and Arlington): 1.2 million
Inner suburbs (Cities of Fairfax, Falls Church, Gaithersburg and Rockville; counties of Fairfax, Montgomery and Prince George's): 3.6 million
Outer suburbs (Cities of Manassas and Manassas Park; counties of Calvert, Charles, Frederick, Loudoun, Prince William and Stafford): 2.1 million
Source: Metropolitan Washington Council of Governments

Arlington County is expected to log about 68,500 new residents, while Prince William and Loudoun counties together will see their populations climb by an estimated 380,100 people.

But the immediate Maryland suburbs -- Montgomery and Prince George's counties, Gaithersburg and Rockville -- are also poised to add plenty of heft to the region's population. The study found that those four jurisdictions will grow by about 420,000 people.

The District's population is expected to increase by about 28 percent to 771,200.

Stewart Schwartz, executive director of the Coalition for Smarter Growth, said that although local governments have been planning ahead, state governments need to focus on looming population increases.

"This is exactly why we argue that where we grow and how we grow -- specifically how we design our communities -- is going to be essential for managing our traffic," Schwartz said. "We can't continue business as usual, spreading out into places with no access to transit and separating homes from work."

Regional leaders said they are prepared for the influx.

"Growth happens whether you want it or not. It's not that we grow, but how we grow," said Sharon Bulova, chairwoman of the Fairfax County Board of Supervisors. "Fairfax County, I think, is wisely preparing for that growth and doing so in a way that is trying to accommodate our future growth in areas that can be supported by mass transit. I think that bodes well for the future of Fairfax."

The analysis predicts the region will also add 1.4 million new jobs.

"A lot of those jobs are intended to be in the service sector: engineering services, management consulting services and things like that," said Paul DesJardin, COG's director of community planning and services. "But there's also a lot of needs that we increasingly see for people with technical training."