GM's biggest brand, Chevrolet, reported flat sales over last year despite new products like the Spark minicar. Silverado pickup sales fell 10 percent.
GM's sales have been trailing the industry all year. They were up 4 percent through October, compared to the industry-wide increase of 14 percent.
Kurt McNeil, GM's U.S. sales chief, and other GM executives tried to explain the automaker's disappointing performance.
GM said its competitors resorted to higher-than-usual incentives last month to get rid of 2012 model-year trucks. GM, which had more 2013 trucks on its lots, was offering $500 less per truck than the industry average. GM has been trying to hold the line on costly incentives, which can hurt resale value and brand image.
"We want to be known for great products, not great incentives," McNeil said.
But some analysts think GM will be forced to offer more deals in December to clear out inventory.
At Ford, sales were up 6.5 percent on the strength of the F-Series pickup. Ford also saw strong sales of its new C-Max hybrid wagon and of the Ford Focus small car.
Some Asian brands got a boost from some unusually big discounts, said Jesse Toprak, senior analyst for automotive pricing site TrueCar.com. TrueCar estimated that Hyundai and Kia, which were admonished by the U.S. government in late October for overstating gas mileage, increased incentive spending by nearly 30 percent. Yet Nissan spending was down 9.1 percent to $2,682 per vehicle.
Luxury cars saw their usual year-end surge as holiday commercials started crowding the airwaves. Porsche's sales rose 71 percent to 3,865, a record month for the automaker. Infiniti, Acura, BMW and Lexus all reported big gains.
Edmunds.com analyst Jessica Caldwell said luxury brands have historically targeted their customers at this time of year because of holiday bonuses. That's no longer a driving factor, she said, but it's still a good time of year for people to buy 2012 model-year luxury vehicles because dealers are trying to clear them out.
Gutierrez said about 70 percent of the vehicles on dealer lots are now 2013 models, so buyers should act quickly if they want a deal on a 2012 model.
If industry-wide sales end up at 15 million for the year, it would be a vast improvement over the 10.4 million during the recession in 2009. Sales would still fall short of the recent peak of around 17 million in 2005.
Other automakers reporting sales Monday:
— Chrysler's sales were up 14 percent. Ram pickups were up 23 percent, while sales of the Fiat 500 minicar more than doubled.
— Hyundai's sales rose 8 percent, led by the Sonata midsize car and the Elantra compact. TrueCar said Hyundai increased incentives by 30 percent it was admonished by the U.S. government in late October for overstating gas mileage.
— Nissan's sales climbed 13 percent as sales of its new Pathfinder SUV more than tripled over last year.