NEW YORK, FEB. 15 -- A federal bankruptcy judge today approved the sale of takeoff and landing rights at National Airport to Northwest Airlines, a move that will double the carrier's activity at the airport.

Northwest's purchase of the 67 slots and five gates from now-defunct Eastern Air Lines will dramatically increase the carrier's employment at National from 170 jobs at present, but a spokesman said the company expected to fill the new jobs with Northwest employees now working elsewhere.

The airline plans to begin expanding its service April 1, and gradually phase in the new flights during that month.

Northwest plans to use its new slots to add flights to Florida and major business centers in the Northeast, in a bid to increase its presence on the eastern seaboard. Northwest General Counsel Richard B. Hirst said the airline wants to use its expanded presence at National to step up its competition with United Airlines, which is the dominant carrier at Dulles International Airport.

"We'll be using the slots in ways that will compete in every way with United from Dulles," Hirst said.

The purchase will also pit Northwest against USAir, the dominant carrier at National with numerous routes in the Northeast as well as direct service to several Florida cities.

Hirst said the acquisition of the National slots -- each of which represents either a landing or a takeoff -- was "very important" for Northwest, which is based in Minneapolis and is the nation's fourth-largest air carrier.

"We don't believe that we can afford to remain a distant fourth carrier in size and strength. In order to prosper in this industry, we need to be the equivalent in strength to American, United and Delta, and, for that, we need a strong route structure on the eastern seaboard," Hirst said.

Although Northwest is short of cash, a spokeswoman said the airline had enough money to cover the cost of the National slots. But it was unclear how much, if any, additional cash the airline might need to buy other Eastern assets. Northwest has said it wants to build a hub at Atlanta's Hartsfield Airport, but has not revealed whether it would attempt to buy any of Eastern's operations there.

It had been widely expected that Northwest would get the Eastern slots, following the Justice Department's announcement yesterday that it opposed the sale of the slots to United on grounds that such a deal would reduce competition at National.

Originally, United had bid slightly more than Northwest -- $35.5 million compared with $35.25 million -- for the slots in the auction being staged by the U.S. bankruptcy court here that is overseeing the liquidation of Eastern's assets. Northwest agreed today to match United's price after the Justice Department's decision.

United made no attempt at today's hearing to block the sale to Northwest, which was approved by U.S. Bankruptcy Judge Burton R. Lifland. As expected, the judge also approved the sale to Delta Air Lines for $5.4 million of the nine Eastern slots at National that Northwest did not buy.

Northwest already has 53 slots and four gates at National, so the purchase boosts its presence to 120 slots and nine gates.

Hirst said it was unlikely at this point that Northwest would attempt to launch a shuttle service to New York based on today's purchase.

"I don't think that there will be a shuttle based on these slots, because we don't have equivalent slots at La Guardia," Hirst said.