The Federal Aviation Administration opened bids yesterday on a project to bridge one of the area's more obvious transportation snafus, the four lanes of speeding traffic that separate National Airport from the Metro subway station there.

The project, a collection of covered escalators and moving sidewalks, would connect the Metro station directly with the North Terminal, about 425 feet away. Thus, a weather-protected traffic-free access between the airport and Metro would be available for the first time.

If the apparent low bid on the project is accepted, construction could begin as early as January. It would take about a year to complete the connection.

The apparent low bid on the project was $3.2 million from the Corning Construction Corp. of Beltsville. That bid is 24.29 percent higher than the FAA estimate of $2.6 million, and that fact presents an immediate problem.

"Anytime something is this far over the estimate we want to double back and make sure that we've taken all cost-cutting measures we can," said James A. Wilding, deputy director of Metropolitan Washington Airports, the FAA agency that runs National. "If I had to guess, I would say that we would go ahead" with the low bid.

Congress appropriated $2.1 million for the project; the balance would have to be channeled from other sources.

The lack of convenient access between the airport terminal and the Metro station has been a source of embarrassment for both federal and Metro officials.

Originally, Metro didn't even plan a station at the airport. That was because someone honestly believed that National Airport would be closed and replaced by Dulles International Airport. When it was decided to build a National Airport station, an enormous row emerged between then general manager Jackson Graham and FAA administrator John H. Shaffer about whether the Metro should be directly underground under the main terminal, or elevated.

Graham prevailed with his elevated scheme on grounds that it would be at least $50 million cheaper and that he could have it in operation in time for the Bicentennial. The station opened on July 1, 1977, one year late. It is almost one-third of a mile from the main terminal, but has nonetheless become popular with air travelers.

The new connector would be compatible with National Airport's long-range plans to expand terminal facilities on a lower parking lot that now rests between the Metro station and the North Terminal. Those plans are in abeyance pending development of a final policy on National Airport growth.