An F20 Tigershark jet crashed on its way to the Paris Air Show yesterday, a possible setback to Northrop Corp.'s intense campaign to persuade the U.S. Air Force to buy some of the fighter planes.

The jet, which crashed in Goose Bay, Labrador, is the second F20 to go down in the last seven months and leaves Northrop with only one of its three prototypes. The first crash occurred during a demonstration flight in South Korea last year.

Northrop spokesman Les Daly said the cause of yesterday's crash, in which Northrop pilot David Barnes, 40, was killed, is not known.

The crash came as the company seemed to be making headway in finding a customer for the plane, in which Northrop has invested $800 million. A key congressional committee last week mandated a competition between the F20 and General Dynamics' F16, a mainstay of the Air Force.

In addition, Air Force Secretary Verne Orr last week ordered the service to include 126 F20s in its five-year budget plans, according to preliminary documents. The action represented the first time anyone in the administration indicated that the F20 might be suitable for U.S. forces.

Northrop originally developed the Tigershark for export, after the Carter administration urged industry to come up with a modern fighter that Third World countries could afford. The Reagan administration has allowed a number of nations to purchase the more capable F16, however, dampening overseas interest in the F20.

As a result, Northrop steadily increased the capability of the Tigershark; the company now says it is "comparable" to the F16. Several members of Congress have urged the Air Force to buy both planes as a way of introducing competition into fighter purchases.

Daly said he would not speculate on the political impact of yesterday's crash, but indicated he does not think it will end interest in the plane. Daly said that, because of U.S. interest in the F20, the lone remaining prototype will not be flown to Paris for the international exposition, which begins May 30.

The F20 that crashed was practicing its demonstration flight during a layover in Goose Bay. The crash in South Korea last year was attributed to pilot error.