Congress has sent the Federal Aviation Administration back to the drawing board on its plans to construct a moving sidewalk between the National Airport terminal and the Metro station that serves it.

In a letter to Transporttation Secretary Brock Adams, House Appropriations Transportation subcommittee chairman Rep. Robert Duncan (D-Ore). disapproved a request to re-allocate $1.2 million in FAA funds to build the moving sidewalk.

Congress already has approved $2.1 million for the connecting sidewalk, but the low bid on the FAA project came in $1.2 million over that. In such instances, the appropriations subcommittee must give its approval before other money can be used to make up the difference.

James Wilding, deputy director of Metropolitan Washington Airports, the FAA office that runs Washington National, said yesterday that "We're going to try and get a new design that has much less automation." The $2.1 million authorization expires Sept. 30.

It is almost one-third of a mile from the Metro station to the main terminal at Washington National, a fact that has become something of a local joke. Nonetheless, almost one Metro rider in 10 who gets on or off the subway at the airport has business at the airport.

The rejected FAA plan called for an automated moving sidewalk that would lift passengers over four lanes of speeding traffic, across a parking lot and into the North Terminal.

The problem with that, according to Duncan's letter to Adams, is that much of the walkway would have to be torn down if the North Terminal were expanded. Such an expansion is part of National Airport's long-range, but unapproved, plan.