The news came as senior European partners in the Airbus consortium indicated they were unlikely to grant British Aerospace a larger stake in the project.
The order for A320s would be Northwest's first large purchase since it went public two years ago, and gives an important boost to Airbus, which has lost out on several recent large contracts.
Northwest also said it has delayed delivery on 16 long-range Airbus A330 aircraft while additional anti-noise devices are installed from engine maker Pratt & Whitney.
Northwest said yesterday that it had signed a memorandum of understanding to buy the A320s, which has been overshadowed by the Boeing 777 introduced last year.
Northwest, already one of Airbus's biggest customers with 66 of the company's aircraft in its fleet, would take delivery of 10 A320s in 1998 and the remainder in 1999. The delivery schedule for the 16 twin-engine A330s has been pushed back five years.
Meanwhile, BAe, which owns 20 per cent of Airbus, would face opposition from its partners and the French government if it tried to increase its stake, according to news agency reports.
BAe may want to raise its stake to 30 per cent as part of a plan to turn Airbus from a partnership into a limited company. Any change requires unanimous consent by the four partners. The statutes specify that Aerospatiale and Daimler-Benz Aerospace hold equal stakes, currently 37.9 per cent. Construcciones Aeronauticas of Spain holds a 4.2 per cent.
Aerospatiale is thought to be particularly resistant to a dilution of its holdings. The French government could also reject any move that would give Britain a bigger stake in Airbus, which is seen as an important national business concern.