DETROIT (AP) _ The paint on Chris Gnapinski's dark blue Ford truck is flaking - again.

The purchasing agent from northern New Jersey is sure the problem is Ford Motor Co.'s fault. His dealer already repainted the front end of the 1989 model and touched up the entire body.

''Now, it's out of warranty and they say they can't do anything about it,'' he said.

But Gnapinski will be back at Elmwood Ford on Monday, this time at the No. 2 automaker's request.

Ford acknowledges a paint defect in potentially tens of thousands of its F- series full-size pickups, the best-selling vehicle in the country for 10 years running and the best-selling pickup truck for the last 15.

But Ford won't recall the trucks, fearing bogus claims that would jam dealer service departments and body shops.

Keeping F-series customers happy is critical to Ford, which annually battles Chevrolet for bragging rights in the last bastion of Big Three auto dominance. Toyota is expected to join the fray in November with an imported pickup.

The F-series is one of the main reasons for Ford's turnaround in automaking profits this year. Through July 20, the F-series had sold 247,736 units, 15.7 percent more than last year.

''Our position on paint is that where people have a paint problem, they raise their hand,'' said Tom Wagner, general manager of Ford's Parts and Service Division. ''We'll take a look at their truck and tell them whether it's their problem or our problem.''

That's not good enough for the Center for Auto Safety.

The Washington-based watchdog group in June threatened to file a deceptive trade practices complaint with the Federal Trade Commission unless Ford agreed to recall and repaint the more than 4 million F-series trucks sold between 1985 and 1992.

The center said that could cost as much as $1 billion. Ford called that figure ridiculously high but did not offer its own estimate.

Clarence Ditlow, executive director of the center, said it has received more than 1,000 letters from Ford truck owners since its June 23 announcement. He said attorneys general from seven states - Illinois, Texas, Maine, Connecticut, Minnesota, Virginia and New York - are considering consumer fraud complaints against the automaker.

''What the letters have done is show us the problem is far more widespread than what Ford is willing to admit,'' Ditlow said.

In 1985, Ford modified its paint with an extra heavy duty coat to help slow rust and corrosion on the F-series truck and several other model lines. Ford also eliminated a conventional paint primer in the process because tests at the time showed this was no longer needed, Wagner said.

But as the sun's ultraviolet rays beat on some F-series models with gray, silver, and light and dark metallic blue paint, the adhesion broke down and began to flake or peel.

Wagner said Ford has been aware of peeling paint on the trucks since 1988, but it took until 1990 to figure out the cause. The company is making changes at all Ford paint facilities to fix the problem, and a primer has been added back into the paint process.

F-series owners never were told of the problem, Ford officials have said, because the automaker doesn't consider it widespread enough.

Ditlow said Ford told some dealers as early as 1987 they might get F-series owner complaints about peeling paint. He alleges Ford covered up the problem by a secret warranty - repainting trucks only for the owners who complained the loudest.

Wagner said Ford officials discussed several solutions, and ruled out a recall.

Instead, the company in mid-July expanded a pilot customer satisfaction program for individual and small business buyers of F-series trucks. A reply card mailed to about 2 million owners of 1987-91 models asks them what problems, if any, they are having. Paint is among areas listed but it is not singled out.

Gnapinski received one of the cards about five months ago. He returned it, listing paint flaking as one problem. Last week, a Ford customer service representative in Detroit called him and set up an appointment for him at his dealer in Elmwood Park, N.J.

''We think we're doing more for the customer in the long run this way than by trying to do a recall on paint,'' Wagner said. ''I'm confident we're going to find the problems.''

Rendle Gallant, body shop manager at Grappone Ford in Concord, N.H., said the paint problems are finding him.

''I've been doing two or three complete paint jobs a week,'' Gallant said. ''It's not unusual to see two people come in at the same time with the problem.''

Gallant said Ford has instructed his shop to charge the company for paint jobs traced to the defect. The average cost is about $1,600.