DETROIT — Thousands of United Auto Workers walked off the job at General Motors plants around the country today in the first nationwide strike during auto contract negotiations since 1976.

A GM spokesman, Dan Flores, said the union launched a national strike after the late morning UAW strike deadline passed without agreement on a new contract, which would include a groundbreaking provision establishing a UAW-managed trust that will administer GM’s retiree health care obligations.

Laborers began picketing outside GM plants.

The UAW has 73,000 members who work for GM at 82 U.S. facilities, including assembly and parts plants and warehouses.

It remained to be seen what effect the strike would have on the automaker and consumers. The company has sufficient stocks of just about every product to withstand a short strike, a senior director of industry analysis for J.D. Power and Associates, Tom Libby, said.

Charlie Coppinger, who has worked at GM’s powertrain plant in Warren for 31 years, walked the picket line along with a handful of others shortly after the deadline passed.

The 51-year-old Rochester Hills resident said he hoped a strike could be settled quickly, but that union members were on the line to back the union and its bargainers.

“We’re just here to support them,” Mr. Coppinger said, adding that leaflets were passed out indicating that the strike was on.

Mr. Flores said the automaker is disappointed in the UAW’s decision to call a national strike.

“The bargaining involves complex, difficult issues that affect the job security of our U.S. work force and the long-term viability of the company. We remain fully committed to working with the UAW to develop solutions together to address the competitive challenges facing GM,” Mr. Flores said.

GM had been pushing hard for the health care trust — known as a Voluntary Employees Beneficiary Association, or VEBA — so it could move $51 billion in unfunded retiree health costs off its books. GM has nearly 339,000 retirees and surviving spouses.

A laborer, Anita Ahrens, burst into tears as hundreds of United Auto Workers streamed out of a GM plant in Janesville, Wis.

“Oh my God, here they come,” Ms. Ahrens, 39, said. “This is unreal.”

Ms. Ahrens has worked seven years at the plant, where she works nights installing speakers in sport utility vehicles. She waited outside the building today for her husband, Ron Ahrens, who has worked there for 21 years.

The couple has three children, including a college freshman, and Ms. Ahrens worried about how they would pay their bills.

“This is horrible, but we’re die-hard union, so we have to,” Ms. Ahrens said. “We got a mortgage, two car payments, and tons of freaking bills.”

More than a thousand UAW workers streamed out of GM’s Delta Township plant near Lansing at 11 a.m. UAW members were handing out picket signs that say: “UAW On Strike.” “I don’t think it’s a win for either side. It’s too bad it’s come to this, but we have given up a lot already,” a quality control specialist who has been with GM for 31 years,
Pat Haley, said.

He said he didn’t have a big problem with the VEBA, but he opposes a possible $5 an hour wage cut and restrictions on vacation time.

While GM has enough cars and trucks to withstand a short strike — the automaker had about a 65-day supply of cars and trucks as September began, a chief economist for the National Automobile Dealers Association, Paul Taylor said — it still would be costly for the company.

The UAW last struck GM in 1998. In that strike, workers at two GM parts plants walked out for 54 days, costing the automaker $2.2 billion. The strike, which occurred between years when national negotiations were held, was over work rules and GM’s plans to eliminate jobs.