LOS ANGELES – To see the constant tension at automakers between sales volumes and profit margins, look no further than the current state of Toyota’s Camry.

The Camry sedan has been the top-selling car in the United States for 11 years. February sales results, however, included a shocker: Camry sales slumped 9.5 percent from a year earlier, the biggest drop in 16 months, knocking Toyota’s sales growth to about half what analysts had estimated.

The rough month reflects rising competition for Toyota, which regained the title of world’s largest automaker in 2012. In the midsize car segment that accounts for 22 percent of U.S. light-vehicle sales, Camry faces models that have been revamped in the past year, including the Ford Fusion and Nissan Altima, which both came with bigger discounts last month, according to researcher Edmunds.com.

While Camry’s sales would have to continue to slide to lose its No. 1 title – it outsold its nearest competitor by 22 percent last year and has kept that same lead so far this year – a swoon for its trademark product would be a blow for Toyota.

“It’s a lot tougher for Camry to maintain the level of dominance that we saw last year,” said Alec Gutierrez, analyst for Kelley Blue Book in Irvine, Calif. “To maintain its dominant position, Toyota’s going to have to look carefully at its incentive approach.”

Across its entire lineup, Toyota’s prices were 5.9 percent higher than in February 2012, the biggest increase of any major automaker, researcher TrueCar Inc. said last month. That compares with an industry average increase of 1.2 percent, according to TrueCar.

Just last month, Toyota finally offered a tidbit: no-interest financing on the 2013 Camry, excluding the hybrid version. The question now is whether it will take an even bigger bite out of its margins to protect the U.S. market-share gains it has made in the first two months of the year.

Of the top four midsize sedans in February, Camry had the second-lowest incentives at $1,505 per car, according to Edmunds.com. Nissan’s Altima offers about $260 more and Ford’s Fusion about $650 more. Honda’s Accord, the perennial No. 2, is also new this year. Honda offered $567 for the Accord that went on sale in late 2012.

Toyota already offered no-interest loans on the 2012 Camry, and in late February extended them to the non-hybrid version of the 2013 Camry.

Honda is benefiting from Toyota’s pricing discipline. Sales of its flagship Accord jumped 35 percent in February. Two months earlier, Camry’s lead over the Accord was fewer than 2,000, and Honda’s compact Civic had even outsold Camry that month as the top-selling car, 33,118 to 31,407.

Ford is also closing in with the redesigned Fusion sedan, sales of which rose 28 percent last month. Nissan’s Altima, the third-best selling midsize car in the U.S. last year, slid 16 percent.

“We know it’s a competitive segment,” said Mike Michels, a Toyota spokesman. “All three of those makes are very high-profile in their marketing, and all three companies want to make an impact with consumers,” he said.

Camry’s February slump comes against a backdrop of a resurgent U.S. auto industry. The three Detroit automakers reported increased sales last month, with General Motors up 7.2 percent, Ford up 9.3 percent and Chrysler up 4.1 percent.

Toyota is also facing mounting competition in China.

The drop in Camry sales may be temporary because Toyota was particularly hurt by the Feb. 16 snowstorm in the Northeast, a region where its models have a higher than average share, according to Jessica Caldwell, an industry analyst for Edmunds.com.

Toyota’s February vehicle sales rose 4.3 percent.

While Toyota’s nationwide market share was 14.4 percent last year, it was 18 percent in the Boston area, Caldwell said.