Girding for the arrival of thousands of new workers along the Baltimore-Washington corridor, Maryland transportation officials are studying ways to build a Metro line between Greenbelt and Baltimore-Washington International Airport.

"It's a concept, not a plan," Maryland Secretary of Transportation Robert L. Flanagan said of the effort, which he called a sign that "Baltimore and Washington are coming together . . . into a single urban area."

At 20 miles, the line would rival the proposed Dulles Airport Metro extension in length and could open, in stages, within two decades, Flanagan said. But much depends on whether the state can persuade businesses along a new route to pony up a large portion of the cost, which could run as high as $2.6 billion.

Metro extensions typically are paid for with state and federal dollars. That makes local funding even more important to backers of a Baltimore-Washington line because any proposal probably would have to compete for federal money with two other proposed extensions, one to Dulles International Airport and one to Fort Belvoir. The Dulles project alone would cost $4 billion.

Other factors that probably would weigh on any decision about a line to BWI include a proposed Purple Line across Montgomery and Prince George's counties that has been debated and studied for many years. Also, a proposed $3 billion intercounty connector highway that would link Interstates 270 and 95 through those counties would require significant federal funding.

"The goal would be to find a way that landowners who benefit from the [BWI] project make substantial contributions to funding and operating the subway line," Flanagan said.

Work on that portion of the concept "is a very critical point early on in the process. You have to have local support."

Flanagan said the department began studying the potential for a new subway line a year ago for two reasons. First was the state's interest in promoting BWI, which it owns. Second was signs of explosive expansion at Fort George G. Meade in Anne Arundel County.

Three years ago, Fort Meade's commander, Col. John W. Ives, convened a working group to develop a comprehensive plan for the base. The plan, signed this week, will not be released to the public, said Meade public affairs officer Melanie Moore, because sections concern force protection plans. She confirmed, however, that the plan foresees the addition of as many as 20,000 jobs to the base over the next three decades, increasing its size by more than half.

In addition, the Department of Defense Base Realignment and Closure Commission recommended in May that several security and information offices be moved to Fort Meade. If the proposal is approved by Congress and the president this year, it would bring 5,300 more personnel to the base over the next six years.

Flanagan said his office embarked on a feasibility study for the line extension early last year because "basically we knew from our conversations and direction" from Gov. Robert L. Ehrlich Jr. (R) "that we expected to be very successful in the BRAC process." The rail proposal was first reported in The Baltimore Sun.

The Army's plan calls for extending the Metro line the 10 miles between Greenbelt Station and Fort Meade. Flanagan said the state is independently considering extending it another 10 miles to BWI.

The feasibility study provided two possible routes, Flanagan said. The first would run along the CSX railroad corridor from Greenbelt Station with stops in Savage and at Arundel Mills shopping mall and BWI. The other would follow the CSX corridor to Savage, Fort Meade and BWI.

MARC trains, which run in the CSX corridor, are running at or over capacity in the area, Flanagan said.

Through a spokeswoman, Anne Arundel County Executive Janet S. Owens (D) said she would welcome the extension. "The county executive has anticipated growth in this area," spokeswoman Jody Couser said. "She calls it the county's Gold Coast because it is so heavy with defense and high-tech, high-quality jobs."

So far, however, there has been no discussion of what portion of the project's cost would come from county coffers, Couser said. Owens expects to receive a formal briefing on Fort Meade's master plan within the next few weeks, Couser added.

Bill Badger, president and chief executive of the Anne Arundel Economic Development Corp., said a public-private partnership should be given serious consideration. "This is really the new paradigm with transportation enhancements because the state has so many needs," he said.

But to persuade county businesses to pay part of the bill, the state would have to prove that a Metro extension would save money in the long run, Badger said.

"We lose so much money and productivity by having workers spending a lot of time in traffic," Badger said. "So if it can be sold as enhancing the bottom line in productivity, companies will understand that. Not to say it's going to be an easy sell."

Badger added: "Without a strong federal contribution, it's just not going to happen."

So far, Metro has not been consulted about a Greenbelt-BWI line.

"We've looked at it informally. If we're going to do an official study, the request would have to come from the Maryland secretary of transportation," said Metro spokeswoman Candace Smith. So far, Smith said, Flanagan's office has not made that request. "We're willing to explore it, definitely," she said. "It would be a big thing."

Staff writer Ray Rivera contributed to this report.