DETROIT - Toyota made a big comeback last month after two years of struggles in the United States, helping the auto industry post its best April results in four years, new figures showed on Tuesday.

Toyota’s sales in the American market increased 12 percent in April, and its market share climbed to 15 percent, the highest point in 17 months, according to The New York Times.

Over all, industry sales rose 2 percent.

Toyota more than doubled sales of its Prius hybrid from a year ago, when prices surged and availability plunged after the earthquake and tsunami that hit Japan. It came within about 1,600 units of outselling the Ford Motor Company, whose sales fell 5 percent.

General Motors had a down month as well, with sales falling 8 percent and its market share dipping to 18 percent from 20.1 percent in April 2011. Having spent the last two years stealing customers from Toyota — first as the Japanese automaker dealt with huge recalls and then after last year’s disasters knocked out much of its production — Detroit will clearly have its hands full again this year, analysts said.

“Toyota’s recovery is ‘mission accomplished,’ much earlier than we thought,” said Jesse Toprak, vice president for industry trends and insight at the automotive research Web site TrueCar.com. “Their buyers are evidently more loyal than we thought.”

Sales increased 20 percent for Chrysler, a slowdown from its recent pace of growth.

Nissan’s sales were flat, and Honda’s fell 2 percent.

Volkswagen reported a 27 percent increase.

Hyundai, Subaru and Mercedes each set company records for April.

G.M. and Ford attributed their declines to fewer selling days this April and reductions in deliveries to car rental companies. But they are also suddenly up against tougher competition from Toyota, which has recently introduced two additional versions of the Prius and a redesigned Camry — the country’s top-selling midsize sedan.

Robert S. Carter, a Toyota group vice president, said those two nameplates were increasingly drawing in buyers new to the brand. But, Mr. Carter said, Toyota is still ramping up production of the Camry and Prius, causing dealers to lose out on some sales.

“Frankly, if we had more Priuses and more Camrys, there’s a bit more volume out there for us,” Mr. Carter said in a conference call with reporters. “We’re having the largest year that we’ve ever had in our history with new product launches.”

Toyota’s performance has surprised many analysts in that it has regained its lost market share without offering big discounts, as carmakers traditionally have done when recovering from a tough period. In fact, Toyota spent less on incentives last month than it did a year ago.

Honda, which also is working to rebound from a bad 2011, increased its discounts significantly with little to show for it. Honda’s incentives as a percentage of vehicle prices reached a record in April, according to TrueCar.

Toyota “did this by the virtue of their products,” Mr. Toprak said. “They’re spending significantly less on incentives than Honda, and Honda hasn’t been able to recover as well.”

Despite its sales decline, G.M. said it was raising its forecast for total industry sales in 2012 by 500,000 vehicles, to a range of 14 million to 14.5 million. Auto sales last surpassed 14 million in 2007.

“We expect gradual improvement in the economy going forward,” Don Johnson, G.M.’s vice president for United States sales operations, said in a statement. “Over time, strength in the manufacturing sector and strong retail sales will lead to more job creation. That will help more consumers put the recession behind them, gain even more confidence and drive vehicle sales higher for both the industry and G.M.”

For the first time this year, gasoline prices ended the month lower than they started it. On Tuesday, the national average price of regular gas was $3.809 a gallon, down from $3.925 a month ago and $3.943 a year ago, according to the AAA motor club.

Gas prices near $4 a gallon have prompted some consumers to buy smaller vehicles, but are not causing overall sales to decline, as happened when prices rose sharply in 2008. Analysts said consumers were increasingly viewing high gas prices as a reason to trade in their current vehicle for a more efficient one.

“Rising gas prices are actually accelerating rather than discouraging new car purchases, as new vehicles have significantly better fuel economy,” Peter Nesvold, an analyst with Jefferies & Company, wrote in a research note.

April had three fewer selling days, excluding Sundays and holidays, than it did a year ago. That much disparity has happened only twice in the last decade, and fewer selling days make it more difficult for automakers to match or exceed their year-ago results.