The Teamsters union, working without a contract since May 21, is set to strike the nation's largest car hauler, Ryder Automotive Operations Inc., at 6 a.m. today, a move that could halt one-third of the new cars bound for the nation's dealers.

Some union leaders have urged a strike against all 17 companies covered by the negotiations, which affect 12,000 workers, including 5,000 at Ryder."I don't think they like it, and I don't like it," said Mike Bane, president of Local 614 in Pontiac, Mich., referring to his 200 members who work for Ryder. Another 400 of his members work for the other car haulers.

"I think if one goes, all should go. It would be more fair, more effective in my mind," he said.

From the managers' standpoint, R. Ian Hunter, executive director of the National Automobile Transporters Labor Division and chief management negotiator, said that, while there has been dialogue about the other member carriers locking out Teamsters if Ryder is struck, current plans do not include a lockout.

Talks broke off Friday evening, and no new talks were set as of midday Wednesday.

The Teamsters said Ryder's position at the bargaining table made it the sole target.

"They have the most financial clout, and they've been using that clout to dominate decisions at the bargaining table," said Craig Merrilees, a union spokesman.

Members of the NATLD make 92 percent of the dealership deliveries nationwide. Ryder, a Troy, Mich., subsidiary of Miami's Ryder System Inc., controls about a third of that market, according to the Teamsters and other industry sources.

Steve Nichols, senior vice president of Ryder Automotive Carrier Group of Ryder System, said the company will do everything it can to serve its customers, but that operating with management or replacement employees is not practical.

"We take the threat very seriously," he said. "Strikes don't help our customers, ourselves or the union."

Mr. Hunter said it's unlikely that other NATLD carriers will be able to handle Ryder's shipments.

"Their equipment capacity is pretty much tapped at this point," he said.

Ted Orme, a spokesman for the National Automobile Dealers Association, said this is a vulnerable time for dealers.

"It's probably our most sensitive time of year for this type of action," he said. "The manufacturers put a lot of money into launch campaigns, and if you can't get supply to back up that campaign, it'll hurt."

Ryder's primary customer is General Motors Corp., which had no comment on the strike threat. Frank DeBartolo, general manager at Celozzi Ettleson Chevrolet-Geo in Elmhurst, Ill., one of the largest Chevy dealers in the Midwest, said 60 percent of his vehicles come by Ryder.

"It's going to hurt," he said. "Inventory is not as plentiful as you'd like. Each model is different. With Cavaliers, we might have a 15-day supply. With trucks and Suburbans, it's a day-to-day supply right now. Chevrolet said they'll do what they can. They'll try to ship the cars in the shortest supply. But 60 percent is a big cut."

Both sides said there was progress during the latest round of talks, which began Aug. 15.

"It's almost incredible; we were so close to settlement," Mr. Hunter said.

Mr. Merrilees said, "It's unfortunate that we're very close, but that stubbornness from Ryder officials is bringing us to a strike."