The auto industry sputtered through its weakest year in nearly a decade in 2020 as the pandemic kept buyers away from dealerships and forced companies to shut down factories for two months last spring.

But automakers are counting on a rebound in 2021, and foresee possibly strong growth in the second half, as they roll out a parade of new sport utility vehicles, pickup trucks and electric cars. Those hopes rest in large part on the expectation that the distribution of Covid-19 vaccines will accelerate this spring and summer after a slow start in recent weeks.

“I am as optimistic as one can be,” Scott Keogh, president and chief executive of Volkswagen of America, told reporters in a conference call on Tuesday. “What is weighing on everything is how quickly can we get those shots rolled out.”

Automakers estimate the industry sold 14.5 million cars and light trucks last year. That amounts to a 15 percent decline from 2019, and the lowest level since 2012, when the industry was still recovering from the financial crisis that forced General Motors and Chrysler to seek government assistance and bankruptcy protection.

Unlike that recession, the difficulties caused by the pandemic did not hit manufacturers and different regions of the country equally. The industry was most severely affected last spring when all North American auto plants were shut down to slow the spread of the coronavirus and many consumers stayed home.

But sales bounced back later in the year in part because of pent-up demand.

G.M. said on Tuesday that its vehicle sales in the United States fell 12 percent in 2020, but increased 5 percent in the fourth quarter from a year earlier. The automaker reported solid performances from its Chevrolet, GMC and Cadillac brands in the final three months of the year. They offset a 10 percent drop in Buick sales.

Over all, G.M. sold 2.5 million cars and light trucks in 2020, down from nearly 2.9 million a year earlier. But the company described its 771,323 sales in the final three months as its strongest fourth quarter since 2007.

“We look forward to an inflection point for the U.S. economy in spring,” G.M.’s chief economist, Elaine Buckberg, said in a statement. “Widening vaccination rates and warmer weather should enable consumers and businesses to return to a more normal range of activities, lifting the job market, consumer sentiment and auto demand.”

Also on Tuesday, Toyota Motor said it sold 2.1 million cars and light trucks in the United States last year, 11 percent fewer than in 2019. In December, however, its sales jumped more than 20 percent, lifted by strong demand for S.U.V.s and pickup trucks. Fiat Chrysler said that its 2020 sales fell 17 percent, to 1.8 million cars and trucks, but that the decline in the fourth quarter narrowed to 8 percent.

Tesla, the world’s most valuable automaker by far, said on Saturday that globally it sold 500,000 cars in 2020, up 36 percent from the year before. The company does not break its sales down by country or continent.

Ford Motor and most other automakers are expected to report their 2020 sales totals on Wednesday.

Because the virus surged at different times in different places, auto sales have also moved in unexpected ways, said Mark Wakefield, a managing partner at Alix Partners, a consulting firm with a large automotive practice.

“If you are an urban dealer, you probably had a lot of disruption, but if you are in a rural area and mostly sell pickup trucks, maybe your sales were only down 5 percent for the year,” he said.

Alix Partners is forecasting that the industry will sell 15.8 million cars and light trucks in 2021. That would be an increase of about 1.3 million but still well below the roughly 17 million level the industry had maintained for several years before 2020.

Mr. Wakefield said a smooth and rapid vaccination effort could give the auto business and the economy additional lift. “If the vaccination rollouts happen well, you could see additional spending get unleashed,” he said.

Forecasters remain cautious because millions of Americans are out of work and under financial pressure. But a significant number of consumers — typically white-collar professionals who have continued collecting paychecks while working at home — have money to spend because they’ve had to cut back on travel, dining and entertainment.

“There is a lot of disposable income out there,” Mr. Keogh said.

Automakers are counting on several new models this year to keep sales on the rise. Ford has redesigned its F-150 pickup truck, the top-selling vehicle in the country, and is bringing back the Bronco, a once popular S.U.V. that the company had not made in years. Ford also recently began delivering the Mustang Mach E, an electric S.U.V. styled to resemble its iconic sports car. Volkswagen plans to start selling an electric S.U.V., the ID.4, in March. And G.M. is planning to reboot the Hummer as an electric pickup truck this fall.

The coming models reflect Americans’ strong preferences for larger, roomier vehicles like S.U.V.s that are classified as trucks and pickups. A decade ago, about half of all new vehicles sold in the United States were trucks. Last year, 75 percent were. Ford and Fiat Chrysler all but stopped making cars, and cars made up only about 10 percent of G.M.’s 2020 sales.

“The love affair with trucks and S.U.V.s just continues every month,” said Marc Cannon, chief customer experience officer at AutoNation, the country’s largest car retail chain. “That’s what everybody is buying now.”