UNFORTUNATELY, the Transportation Department's final plan for National Airport starts with the premise that National is, and always must be, Washington's primary airport. That premise is, and for years has been wrong.

While the plan does set a limit where there was none before and it does diminish the number of flights by the big jets, the airport will be allowed to grow slightly and it will serve more distant cities. What this means is that the quality of life for the thousands of people who live in the "sewer of noise" around the airport has been traded off for the convenience of those who travel by air.

In devising this plan, Secretary Neil Goldschmidt found himself refereeing several quarrels. National's neighbors resent the noise and want operations restricted. Passengers -- the most vociferous and influential of whom have been members of Congress -- count the convenience among their "perks" and want operations expanded, irrespective of the damage to the enviroment and well-being of the city they are temporarily parked in. More local inhabitants will be disgusted than will be astonished by news that the new rules will allow non-stop flights to New Orleans -- an executive branch kowtow to Sen. Russell Long, chairman of the Finance Committee. Mr. Long will now be spared the excruciating ordeal of having to make a stop on his way home.

Then there's the related quarrel over the physical expansion, with the airlines pushing for endlessly bigger facilities and most of the enviromental considerations pushing back. There's also a quarrel among airlines over which kinds of service are to have how much of the schedule.

Mr. Goldschmidt has tried to include a little something for everyone. For residents complaining about noise, his plan reduces the number of landings and take-offs by jetliners from 40 to 36 an hour. The much-infringed curfew at 10 p.m. will be more heavily enforced, with the airport to close unconditionally at 11 p.m. But in return, the airlines will be given permission to bring wide-bodied airliners into National -- meaning more passengers with fewer flights.

Mr. Goldschmidt has also established a ceiling of 17 million passengers a year through National. The current flow is about 15 million and, without a limitation, it would have risen to perhaps 19 million by 1985. The ceiling serves notice to the airlines that most of the expansion of service into the Washington area will have to go through Dulles or Baltimore-Washington International. That at least establishes a horizon, for both the airlines and the Federal Aviation Administration, for planning and construction at National. And the plan does acknowledge the need for better transportation between the city and Dulles. But the fact is the trend in numbers of passengers using National should be down, not up.

Mr. Goldschmidt left one difficult question open for consideration. If the number of landings is limited, which airlines will have the right to them? In the old days, when the government regulated routes, only a few airlines came into Washington and they divided up the schedule among themselves. But deregulations has brought many more players into the game, all clamoring for slots in the sc hedule. The old system of negotiation is collapsing. Probably the simplest and best solution is to auction off landing rights to the highest bidder. That threatens some of the smaller lines and routes to smaller cities. But Mr. Goldschmidt has provided them with at least a measure of protection through special provision for commuter service.

To sum up: this is less than thrilling news for the metropolitan area. The scale of operations at National should have been reduced. Pressure from the Capitol won out. A firm limit on use, not much above the present level, is a very distant second best.