When the McLean Trucking Co. shut down for good last week, more than 9,000 drivers, mechanics, and other employes were abruptly thrown out of work in the largest bankruptcy in the history of U.S. trucking.

That might have seemed a significant enough milestone, but in an industry buffeted by five years of economic turbulence, the death of the Winston-Salem, N.C.-based company also took on larger symbolic meaning. McLean, industry officials asserted, is the most dramatic casualty to date of trucking deregulation, the latest of more than 4,000 trucking company failures since 1980 caused by cut-throat competition.

Moreover, industry lobbyists quickly moved to capitalize on the demise of the nation's fifth-largest trucking firm. In recent months, the industry, along with the Teamsters union, has geared up to fight the Reagan administration's recent proposal to complete the deregulatory process and strip trucking of its last few Interstate Commerce Commission-enforced protections, including its limited immunity from antitrust prosecution.

"The McLean thing falls right into the scenario," Thomas Donahue, president of the American Trucking Associations, said in an interview this week. "This industry is in serious financial condition -- in the first quarter of 1985, 45 percent of our companies lost money. . . . To go forward with further deregulation at this time -- even the perception of it -- would create a serious trauma. . . . The sensitivities are that great."

"Anybody who thinks we need more competition doesn't know what's going on in the world," added Steve Murphy, senior vice president of Yellow Freight Systems Inc., the country's second-largest trucking firm.

Reagan administration officials contend -- and most economists agree -- that trucking deregulation has produced greater efficiencies and significantly lower shipping rates. The extent to which the McLean failure typifies the larger problems of the industry also is subject to debate. In contrast to McLean, the country's two top trucking firms, Roadway Express Inc. and Yellow Freight, both reported increased profits during their most recent three-month filing with the ICC.

Perhaps even more significantly, say some analysts, there was at least one "wild card" in the McLean bankruptcy, and that is the role of a little-known, billionaire Lebanese businessman named Issam Fares, who bought McLean for $102 million in 1982 and then pulled out, or appeared to, just a few months before the final crash Jan. 10.

Whether Fares could have saved the company -- or even if he still owned it -- was unclear to company officials as they began the painful process of liquidation this week. "He's a mystery man, nobody knows that much about him," said E. R. Brenegar, McLean's vice president for personnel, when asked about Fares.

Best known for the red diamond emblems on its trucks, Mclean has been a fixture on the highways since 1934, when it was founded by shipping magnate Malcolm McLean, now president of the U.S. Lines shipping company. But with the onset of deregulation in the early 1980s, the company's profits nose-dived as it was hit by the same economic forces sweeping the rest of the industry.

In particular, a flood of new low-cost operators entered the trade, many of them individual entrepreneurs who hocked their homes, bought trucks and hit the road. That development, combined with the recession of 1982, produced price wars and special discounts that put the squeeze on McLean.

"There was pricing that was just atrocious," contended Brenegar. "It was based on whatever they can get. It was, 'Let's Make a Deal' out there."

The price-slashing started a self-perpetuating cycle: Lower revenue made it difficult for McLean to maintain its aging truck fleet, resulting in reduced maintenance, leaky trucks and higher claims by shippers against the company for damaged goods. While larger operators were able to generate the outside capital to buy new trucks, and smaller operators only had one-truck fleets to keep up, middle-size McLean found itself in a bind.

And then came Fares, who is believed to have close ties to the Saudi royal family. Fares has homes in Athens and Riyadh, Saudi Arabia, from which he operates an international financial empire that does extensive business in the Mideast. His most prominent interest is Minefa Holdings, a Dutch construction conglomerate. But according to a Securities and Exchange Commission filing, Minefa is owned by Issam Investments N.V., a Dutch Antilles-registered company with interests in petrochemicals, food processing, specialty chemicals and many other areas.

According to the SEC filing, one of Fares' wholly owned subsidiaries, the Houston-based Wedge Transportation Co., bought McLean in 1982, a development that boosted morale at the Winston-Salem headquarters. But the hopes that Fares would pour money into the ailing company were quickly dashed, and he never showed up at the company. After McLean reported $30.5 million in losses during the first six months of 1985, he was apparently ready to unload it.

Attempts to reach Fares or an aide were unsuccessful.

As part of a last-ditch cost saving plan in the fall, Wedge agreed to give up 57 percent of the stock in McLean to its employes, including 12 percent to the officers and 45 percent to the workers, said Brenegar. But the employe-ownership plan, to be phased in over five years, was contingent on a 15 percent pay cut -- a particularly painful pill for the workers to swallow since wages had been frozen for three years.

Still, the employes bought in, and hopes were running high until last week when Citicorp Industrial Corp., one of McLean's principal lenders, cut off its line of credit, precipitating the final collapse.

But given the five year phase-in for the stock transfer, the big question mark appeared to be who will now be liable for the company's debts. "It's unclear who really are the owners here and who will be liable," said R. V. Durham, president of Teamsters Local 391 in Winston-Salem. "That's probably what the lawyers are going to be debating in bankruptcy court."