The Detroit automakers and the United Automobile Workers continued to negotiate on Saturday, company representatives said, a day after the union expanded strikes in a way that could curtail the supply of spare parts for vehicles made by General Motors and Stellantis, which owns Jeep and Ram.

U.A.W. members walked off the job at G.M. and Stellantis parts distribution centers on Friday but spared Ford, saying the company had done more to meet its demands.

“Our pressure on Ford is starting to pay off,” the U.A.W. told members Saturday.

While there was no indication a deal with Ford was imminent, an agreement with the company could put pressure on the other two to offer similar terms and lead to a speedy end to the strike, analysts said.

“The moment you get a deal with Ford that includes much or all of what the U.A.W. is looking for, that puts a lot of pressure on G.M. and Stellantis,” said Michael Duff, a professor at the Saint Louis University School of Law and a former attorney for the National Labor Relations Board. “They are putting them in a position of having to argue why they’re different, why they can’t give anything more.”

A short strike would be good news for the economy. About 200,000 people work in auto manufacturing, according to the Alliance for Automotive Innovation, an industry group. That figure does not include jobs that are indirectly dependent on car making, which is several times higher.

Lost wages would hurt consumer spending, while inflation could rise if some vehicles become hard to get, or repair shops and dealerships run short of spare parts. If so, the Federal Reserve would have to continue its efforts to slow the economy by keeping official interest rates high. More than 18,000 U.A.W. members are now on strike.

The auto companies also face pressure from public opinion. The autoworkers’ argument that their wages have not kept up with inflation, while carmakers have reported healthy profits, resonates with the public, said Ivana Delevska, founder of Spear Invest, an investment firm.

“Inflation is up across the board. They need to pay their cost of living,” Ms. Delevska said of workers.

Polls show that the workers have public opinion on their side, but that could shift if a long strike makes it hard for people to get their cars fixed or is perceived as damaging the economy, Mr. Duff said. “As the strike drags on, you can have disillusionment with workers,” he said.

Stellantis workers walked out at 20 of the company’s parts distribution centers Friday, while G.M. workers went on strike at 18 centers.

A deal that Ford reached this past week with the union that represents its Canadian workers could offer clues to the outcome in the United States. The deal with Unifor provides for pay increases worth up to 25 percent over the three years of the contract, as well as bonuses, improved retirement benefits and measures to protect employees as Ford retools factories for electric vehicles.

Unifor, which probably has less leverage than the U.A.W. because Ford has a much smaller presence in Canada, achieved those gains without having to walk out. The union is negotiating separately with G.M. and Stellantis in Canada.

Investors are expecting the carmakers and the unions in America to agree on a wage increase of less than 30 percent, Ms. Delevska said, who added that both sides have an incentive to settle quickly. “It’s in nobody’s best interest that this extends much longer,” she said.

The U.A.W.’s demands include a 40 percent wage increase over four years, improved retiree benefits and shorter work hours. The union also wants an end to a tiered wage system that starts new hires at much lower wages than the top U.A.W. pay of $32 an hour.

Ford agreed to some of the U.A.W.’s demands, according to the union, for example promising to adjust workers’ pay in step with inflation and increase their profit-sharing bonuses.

Ford also agreed to give workers the right to strike over plant closings, an important concession. The union is worried that carmakers will shutter some factories as the industry shifts to electric vehicles, which require fewer parts and labor.

“These are historic gains,” the U.A.W. said Saturday in a message to members, “but we have further to go.”