THERE ARE some U.S. senators circling over National Airport trying to pass legislation that would make the place noisier and more congested. Given the history and geography of the terminal, this is a terrible idea, but sponsors of the bill have couched it in a call for more competition -- make that read flights by home-state airlines or flights to and from home states. The real effect would be to undo a delicate agreement that at least has maintained some reasonable limits on the already busy airport. There is no good reason for Congress to wreck this arrangement.

The bill is sponsored by Sen. John McCain, Republican from Arizona, which just happens to be the home of America West -- which just happens to be one of the airlines seeking a bigger share of the Washington market. The proposal would remove federal limits on the number of airline flights per hour at National as well as at LaGuardia, JFK International and O'Hare. Since 1969, the Federal Aviation Administration has limited the number of scheduled passenger jet flights at these four heavily used airports to reduce excessive delays. The limit at National is 37 flights an hour. The FAA also allocated landing rights among the airlines using these airports. It allows carriers to buy and sell these "slots," which has been a source of complaints from excluded airlines.

The McCain bill would eliminate the limits on the slots, adding more for new entrants and prohibiting the buying and selling of slots. That has a fine competitive ring to it but is wrong for National -- which is just undergoing improvements to accommodate the traffic it now must bear. Noise and safety concerns would be serious, as would strains on terminal capacity.

Congress was right when it agreed with the Reagan administration that National and Dulles would be better run by a regional authority. That authority already is moving to build a new, safer and more suitable terminal closer to Metro and with more parking. The last thing the airport needs is a flood of new traffic imposed by congressional interests.