CHICAGO -- Say, have you heard the one about three drunk pilots?

The nation's commercial pilots have, indeed, heard the joke, but they're not laughing. Instead, they're launching an advertising blitz to convince the public that airline pilots are professionals, not fodder for Johnny Carson's monologue.

The Air Line Pilots Association, the national union for commercial pilots, is asking its members for "generous, voluntary" donations to fund a "pilot image enhancement program."

That's a buzzword for television and radio commercials to "enhance the public image of an airline pilot."

The union's recorded hot line message for its members, which outlines the ad program and makes a pitch for members to contribute, cites "deregulation and a series of incidents" that have led to "unfavorable and often undue criticism in the public eye" as the reason for the ads.

But it's clear that the most embarrassing incident was the arrest of three Northwest Airlines pilots accused of being drunk while flying from Fargo, N.D., to Minneapolis on March 8.

That flight quickly turned into a cottage industry for the nation's comedians.

The Federal Aviation Administration would not have caught up with those three if they hadn't been riding around on the baggage carousel, one joke goes. And, you know why that flight had three pilots? Because they don't like to drink alone. Oh, and, the pilots delayed landing for a while; they had to wait for the airport to stop circling.

Northwest, which immediately fired the three, steadfastly has said the company is taking the jokes in stride and that the flying public recognizes the incident as a bizarre, one-time occurrence.

But six weeks later, another Northwest flight was delayed because a pilot refused to fly after a passenger accused him of being drunk. That charge turned out to be baseless. Drinking also was suspected, but not proved, in the case of a USAir flight that slid into New York's East River in 1989.

The pilots union clearly has decided the public isn't taking the original incident in stride. The union has produced six 60-second radio commercials and one 30-second TV spot and is seeking money to pay for broadcast time.

On its recorded message, the union suggests "guidelines for contributions" by its members. A captain at a major airline should kick in $250, the union suggests, while a first officer should contribute $150 and a second officer $50.

"Of course, donations of any size will be appreciated," the recording says. The average base pay of an airline pilot is upward of $80,000, according to industry figures.

The union's national headquarters in Washington did not return telephone calls.

The three former Northwest pilots are due in court in late July. They are Capt. Norman Prouse, first officer Robert Kirchner and flight engineer Joseph Balzer. They face several state and federal charges.