or at least people have been saying so for a good 20 years now -- when Dulles Airport will blossom into a honest-to-goodness, busy-all-the-time transportation terminal. And whatever else it may take to make that happen, one ingredient will have to be a fast and convenient link between the planes and downtown Washington. Transportation experts have been talking about what to do in the way of mass transit but the conversations generally end at the mention of money. That is why Greater Washington should be more than a little interested in what a group of private investors is proposing to build between the West Falls Church Metro station and Dulles.

Washington lobbyist Robert K. Gray, former Organization of American States secretary general Alejandro Orfila and two Dulles-area developers are among those who have formed a company called Dulles Access Rapid Transit -- DART -- that seeks to build a 16-mile light-rail line if the right agreement can be struck.

The group has asked the Federal Aviation Administration to lease it the median strip on the Dulles Access Road as well as 600 acres at the airport that would be subleased to developers for office buildings, hotels and other projects to finance the rail line's construction. The current cost estimate is $300 million -- and it is on this figure that success or failure is likely to hang. How good is that number, and what does it include?

Other questions yet unresolved publicly include just what kind of service would be provided along the route. Would there be stations to serve the neighborhoods there? If so, how many? And what would this do to the time and costs of the project?

Virginia congressman Frank Wolf, who has made it his business to monitor all forms of transportation throughout the region, says he's pleased by this new interest on the part of the private sector but won't endorse any particular rail plan without a federal study of everything involved. His point is a good one. Such a study is expected to begin this spring, anyway.

It may well turn out to be cheaper to run buses up and down the corridor every 30 seconds. As for the rail proposal, everyone deserves a much clearer idea of what kind of development is envisioned at the airport. Still, any hopes for massive federal aid for this kind of project are slim to zero right now -- so DART, with its private money, is all the more attractive.