Gov. Martin O'Malley (D) left no question about his vision for the Purple Line, announcing plans in a news conference Tuesday to lobby Congress for money to build a $1.5 billion above-ground train line connecting Bethesda to New Carrollton.

The planned mass transit line, which has been debated in Montgomery and Prince George's counties for more than 20 years, could begin carrying passengers as early as 2016, though state officials say it is more likely to come by 2020. The timetable depends entirely on the ability of the federal government to provide funding for construction.

The announcement by O'Malley at the New Carrollton Metro Station marks the first firm commitment the state has made to making sure the Purple Line uses trains rather than buses. It came the same day that the governor announced plans to seek federal funds for the Red Line, a proposed $1.6 billion train route connecting east and west Baltimore.

State officials were unable to say how much of the rail funding will come from the federal government.

The Purple Line is slated to go from Bethesda to New Carrollton, with stops in Bethesda, Silver Spring, Takoma Park, Langley Park, Adelphi and the University of Maryland, College Park. Planners hope to install a secluded pedestrian and bike trail to run alongside the light rail trains.

"These trains are narrow and sleek, quiet and low to the ground," O'Malley told the crowd of about 75 residents, elected officials and advocates. "This is a modern light rail."

Supporters say the system will provide economic, environmental and public benefits. For the first time, riders will be able to travel alongside the Capital Beltway route without taking the Metro into Washington, D.C., to go to Montgomery and Prince George's counties. Officials hope the project will ease congestion on the Beltway.

Longtime advocates for the Purple Line wore purple outfits, waved signs and cheered the governor during his remarks.

"This connects real communities that are already here," said Barbara Sanders, a Silver Spring resident who has lobbied for the line for two decades. "And we'll be able to walk beside it. It's a local option."

O'Malley's decision to take the train route over buses follows recommendations adopted by both Montgomery and Prince George's County Councils, though some residents in Montgomery had preferred using buses on a dedicated road instead because of the lower costs.

Bus supporters also worried the train lines would divide properties and that having walking trails next to rail cars would lead to accidents.

Referencing the contentious debates over the project, O'Malley said the design benefitted from public discussion.

"It's time to move forward as one Maryland," he said. "I ask for your continued partnership and your continued dialogue."

The most vocal opponents in the town of Chevy Chase are reportedly considering filing a lawsuit against the state over the rail option.

Prince George's County officials cheered the announcement, which reaffirms longstanding goals the council set in 2002.

"Our point for years has been to start it here, that we're on board. We've been on board," said Prince George's Council Vice Chairman Thomas E. Dernoga (D-Dist. 1) of Laurel. "It's exciting to know that now we've all reached agreement."

Prince George's officials are already laying plans to extend the transit line south to the National Harbor development at the Potomac River.

"That will be a lot easier to do when this is built," said David Byrd, deputy chief administrative officer for government operations/environmental services, who heads infrastructure development for the county government.

Both governments have been waiting since February for O'Malley to make a commitment to the light rail option.

Montgomery officials also applauded the announcement and pledged that the rail line will not disrupt hikers and bikers.

"We will continue to work to preserve our beloved Capital Crescent Trail," said Montgomery County Executive Isiah Leggett (D).

The state already has allotted money to plan for the line, and much of the land where it will run is state- or county-owned. The real hurdle is getting money for construction, officials said.

Congresswoman Donna Edwards (D-Dist. 4) of Fort Washington, who said she was late for the news conference due to Beltway traffic, pledged to include both the Purple and Red lines in the upcoming transportation appropriations packages moving through Congress.

"I just wish I had the Purple Line this morning," she said.

Though state officials deny any competition exists, the two rail projects have been seen by some officials as potential competitors for federal dollars and dividing the interests of the Washington suburbs and Baltimore city regions.

Both massive projects must be built, said Beverley K. Swaim-Staley, acting secretary of transportation for the state.

"I don't believe we have any choice but to push for both," she said. "We have to be proactive. Each of these projects is vital to their region."

The secretary was unable to say how much the state would have to spend on the projects or whether fares would be higher to support the project costs.

"It's too early," she said.

Congress is currently in recess and will not take up transportation funding until at least the fall.

E-mail Daniel Valentine at dvalentine@gazette.net