Maryland Gov. Martin O’Malley (D) on Friday moved to seek federal backing for an $800 million rapid-transit bus system to connect the state’s surging population and technology corridor along Interstate 270 to the Metro system.

As envisioned, the route would extend the current end of the Red Line in Shady Grove for 15 miles, into northwest Montgomery County and almost halfway to Frederick. Buses would operate in a dedicated new lane, separated from existing traffic, and connect federal facilities, corporate headquarters and residential town centers from just outside the beltway to just north of Germantown.

O’Malley’s decision all but ends years of debate about whether the so-called Corridor Cities Transitway, or CCT, should be operated by bus or more expensive light rail. Even in its more frugal form, however, the route adds a third major Maryland transit project to already stiff competition for federal transportation dollars.

The announcement also highlights anew Maryland’s nearly bankrupt transportation trust fund. O’Malley this year failed to persuade lawmakers to approve a gasoline sales tax to replenish the account. Without some form of new revenue, Maryland in coming years will not be able to afford even one of its three major transit plans. A proposed Purple Line connecting Montgomery and Prince George’s and a planned light-rail line in Baltimore would each cost roughly $2 billion.

“This is a very first step,” Maryland Transportation Secretary Beverley K. Swaim-Staley said of the bus route. “It is another need that we have now identified, and we will have to figure out how in the future to pay for it.”

Swaim-Staley, who recently announced she is leaving her post, said she is nonetheless confident that the bus line stands a good chance to win federal backing, in part because it will be less complicated than a rail project, and would be built mostly along roads where the state already owns right-of-way.

According to Friday’s announcement, the state will submit the project to the Federal Transit Administration under its New Starts Program this summer. If approved, the state could begin preliminary engineering in roughly a year, Swaim-Staley said.

Depending on funding, construction could begin in 2018 and the line could be in service by 2020.

Montgomery County Executive Isiah Leggett and county council members who early this year reversed course and endorsed the bus line, praised the state’s decision Friday, saying construction as soon as possible will be critical to the county’s planned growth.

The county cannot proceed with its long-term plans to develop an area in Gaithersburg for science research, known as the Great Seneca Science Corridor, without the bus line because much of the approved denser zoning for the area is dependent on having access to public transportation.

If built, the line would be Maryland’s first rapid-transit bus line. State officials offered no estimate Friday of how much tickets to ride the line might cost.