As the two debilitating strikes at General Motors' parts plants in Michigan head for their eighth week, attention is shifting from the car- and truckmaker's largely shuttered North American production facilities to its dealers' lots.

Here, the situation is more complex than on the production side but hardly more encouraging. Many dealers say that when the strikes started in early June, they were well stocked, partly in preparation for GM's regular summer production shutdown. But with a lack of deliveries since then, this buffer is steadily eroding, and the prospect of empty showrooms may be only weeks away.Thomas Pontiac, a South Holland dealership in Chicago's southern suburbs, says it is down to one Grand Prix, one Grand Am and a couple of Pontiac Bonnevilles, plus a handful of 1997 models. That is approximately one-third of its normal inventory.

The dealership, which handles vehicles made by a number of other manufacturers besides GM, says the lack of fresh GM supplies has even affected its stocks of non-GM cars - notably Hyundai models and Nissan Maximas.

"People are switching to what they can get," says one salesman.

A few miles west, Bridgeview's Rizza Chevrolet, which carries the carmaker's popular sports utility vehicles and trucks, says it has received no new vehicles for a month and admits stocks have fallen. But it also maintains that the relatively high inventory of GM vehicles it was carrying when the strikes started still provides a valuable shield: "We were well stocked up," it says, "so it's not a situation where we're out of any models."

Like the Pontiac dealership, it, too, has noticed a change in customer buying patterns: "We're not selling that many new cars - we're selling more used cars," says one manager.

Why this might be is unclear, but he suspects that some potential buyers aren't even making the trip to the showrooms at present. "People know about the strike. They may be postponing purchases."

That is precisely what worries GM. The carmaker - whose North American market share going into the strike was about 31.5 percent - says there are still 600,000 cars and trucks on dealers' lots across the country, and the public perception that dealers have run out of GM vehicles is misplaced.

It acknowledges that there are "pockets" where shortages may be occurring but says these are mainly in urban centers or areas where there are large numbers of GM employees, such as Detroit and other Midwest cities.

GM's answer is a new television advertising campaign, the key message of which will be that there are still "lots of cars" to be bought.

That initiative is welcome, according to the Florida-based Republic Industries, which has built itself into one of the nation's largest car dealership groups through a quick acquisition program.

But the company, which owns about 65 GM dealerships alone, still warns that anyone whose heart is set on one of GM's "hot" models such as the Chevrolet Tahoe sports utility vehicle will probably be disappointed: "We've got plenty of cars, but if you're in the market for the hot products, you'll have difficulty anywhere."

And like most dealership owners, big or small, Republic warns that time is running out for GM - particularly since any settlement between union and management would still need worker ratification and then involve a further lag before production restarted and cars were delivered.

"If the strikes were to continue beyond this month, we would not be in such an enviable position," it confesses.

Marshall Cogan, chief executive of the United Auto Group, another of the quoted dealership companies, is even more blunt. "If the strikes last into August, we'll be out of cars in September," he says.