Although the Firestone Tire & Rubber Co. is faced with the biggest produce recall in history because of problems with its 500 steel-belted radial tires, no one -including the government - has been able to say just what is wrong with the tire.

The irony is chilling to the company when it is realized that recall - which government sources say may come as early as this week - could cost Firestone $100 million or more, according to industry analysts.

Yet the federal government is poised to order such a recall of about 13 million of the tires sold within the past three years and still on the road, citing what it claims is overwhelming evidence that the tire has failed in record numbers - causing hundreds of accidents and dozens of deaths and injuries.

Indeed the National Highway Traffic Safety Administration last July made a "preliminary determination" that the 500 - which was produced from 1972 until early this year - has an unspecified design flaw causing a disproportionate number to experience blowouts or tread separations.

And an investigation by a congressional subcommittee revealed that one out of every 11 Firestone 500 tires ever made suffered tread separations, "a type of tire failure that frequently leads to blowouts."

The report, issued on Sept. 1, followed several days of hearings by the House subcommittee on oversight and investigations, chaired by Rep. John Moss (D-Calif.) It also disclosed that one out of every six Firestone 500 owners had returned their tires because of consumer problems. It said this was rate "considerably higher than the 7.4 percent adjustment (return) rate previously disclosed by Firestone."

The report alleges that Firestone knew of consumer problems with the tire long before the government did, but failed to warn either the government or consumers.

NHTSA also released Firestone documents at its hearings on the tire last month revealing that in Jan. 1977 Firestone was forced to pay Montgomery Ward an extraordinary $500,000 payment to compensate problems that retailer was experiencing with the steel belted 500 radial tire made by Firestone under the Ward label.

But throughout the controversy, no one has been able to pinpoint where the safety problem lies.

While NHTSA points out that under present law, it can recall the tire merely on the basis of consumer complaints of large numbers of failures, Firestone and some tire experts have said that such a ruling is unfair.

All along, Firestone has contended taht the cards are stacked against it. Consumer complaints run higher on the 500 because the company has a "liberal return policy," company officials (See FIRESTONE, D10, Col. 1) (FIRESTONE, From D7) said. Plus, they add, growing publicity about the problems of the tire have caused consumer complaints to snowball.

"The tire contains no safety-related defect of the kind now sought to be established through what is claimed to be a comparison with the performance of other tires of similar construction," Firestone attorney Patrick McCartan told NHTSA hearings last month. The tire is "comparable in every essential respect with the first generation steel-belted radial tires of other manufacturers," he said. The company has also claimed that the problems are due to consumer failure to keep the tires properly inflated.

And the Akron Beacon-Journal reported last week that a confidential independent test of 16 different tires done for 16 tire companies in 1976 revealed that the Firestone 500 "did as well as, in some cases better than," every other tire tested for performance.

The study by Smithers Scientific Services, Inc., an Akron firm, was financed by the participating firms which paid $6,000 each for their tires to be tested and a copy of the report.

But despite Firestone's public statements that it is standing by its tire, which it calls "safe and reliable," Washington attorney Clark Clifford has been quietly negotiating with NHTSA in an effort to limit the recall now considered imminent. Clifford was hired by members of the Firestone family after negative publicity continued to mount against the company.

Firestone fought at every turn government efforts to investigate the problem, according to federal, officials. A court order finally forced Firestone to turn over some 30 million documents to the government - the last batch of which were delivered to Washington in a moving van last week. The company still will not grant interviews with reporters.

Now, the company is trying to limit the recall by negotiation. Sources say the company is trying to break down the production of the tire into three limit the recall to the earliest model.

That first model used a 5-rib tread design, which according to the Moss report was, by far, the design with the most problems. The overall adjustment [return] rate on the 5-rib models was a whopping 26 percent, or one in every four tires sold.

The second model, or second generation steel belted 500 used a 7-rib tread design, and saw the adjustment rate drop to 9.7 percent, according to Moss.

The third type of tire is one that has the 500 brand on the body of a newer technology tire now called the 721, which uses seven strands of wire around two others wrapped by one. There are no available adjustment figures on this newer tire.

Company officials claim that about one quarter of the tires on the road are of the 5-rib design, or 2.4 million tires. The 5-rib design, was produced from 1972 through 1978. Despite the fact that later technology tires like the 7-rib began being produced as early as 1974, the tire industry traditionally takes a long time to phase in and out new and old tires. There are frequently long periods of time when production of two different generations of the same tire overlap.

"Oh they will survive the recall," said one industry analyst who asked not to be identified. "But they better get into some new lines of business because they will have to go a long way to restore their image. People like to think they are driving on safe tires, and that is one product they don't want to take even the slightest chance on. How many times have you seen expensive new tires on old clinkers of car?"