LOS ANGELES – Toyota Motor Corp.’s Camry in March ceded its rank as America’s best-selling midsize car for the first time in 17 months, slipping behind Nissan Motor Co.’s Altima and losing share to Honda Motor Co. and Ford Motor Co. models.

Camry sales in the U.S. declined 12 percent to 37,663 units last month, or 100 fewer than the Altima, whose deliveries declined 8 percent, according to company figures.

The two midsize sedans lost market share to Honda’s Accord and Ford’s Fusion. Accord sales climbed 36 percent while Fusion sales were up 6 percent.

Toyota’s flagship sedan has been the country’s best-seller every year since 2002, but U.S. automakers are fielding their most competitive cars in decades.

At stake is supremacy in the biggest segment of the U.S. auto market at a time when demand is pushing light-vehicle sales to their highest levels in more than five years.

“Toyota may not have realized just how competitive the segment would get,” said Alec Gutierrez, industry analyst for auto-market researcher Kelley Blue Book. “This is the best-selling segment in the U.S., and the surge will continue for the rest of the year.”

Demand for midsize cars, along with pickup trucks from U.S.-based Ford, General Motors Co. and Chrysler Group LLC, drove up U.S. auto sales 3.4 percent to the highest since August 2007.

“Long gone are the days when you saw Camry as the perennial winner by a big margin,” Al Castignetti, Nissan’s vice president of U.S. sales, said Tuesday. “We’ll all fight for that pie, and it will be more of an equal pie now that we’ll all share in.”

While the Altima topped Camry’s U.S. sales last month, the Nissan model ranks only third in the segment this year. For the first quarter, Toyota’s Camry is more than 12,000 units ahead of its nearest competitor, Honda’s restyled Accord. The Fusion, redesigned in late 2012, ranks fourth this year.

“We have Camry right on plan, and we feel really good about our position,” Bob Carter, Toyota’s senior vice president of U.S. sales, said Tuesday. “We’re absolutely confident we’ll continue to be the No. 1 vehicle in the market in 2013.”

Toyota, the world’s largest automaker, saw its total deliveries of Toyota, Lexus and Scion models increase 1 percent in March, missing the 1.6 percent increase predicted by analysts in a Bloomberg survey.

Prius hybrid sales dropped 23 percent, Toyota said. The Prius decline resulted from a combination of less aggressive marketing last month and a drop in fuel prices, Carter said.

Toyota will continue its current no-interest loan offers and discounted leases for the Camry and other models for another month to sustain sales, he said.

Nissan, Japan’s second-biggest automaker, reported a 1 percent sales gain, beating the average estimate for a 2.1 percent decline. Deliveries of Nissan and Infiniti brand vehicles totaled 137,726, the most ever for the month of March, the company said.

Honda, Japan’s third-largest automaker, said it sold 136,038 Honda and Acura brand autos, up 7.1 percent. While that was the biggest increase among major automakers in the U.S., it trailed an expected 8.5 percent gain for the company.

Unlike major competitors, Honda doesn’t have a program to sell its vehicles directly to rental or business fleet customers. On that basis, the company estimates it outsells rivals to the Accord, Civic, CR-V sport utility vehicle and Odyssey minivan, said John Mendel, Honda’s executive vice president.

“It’s particularly rewarding to see Accord and Civic winning new customers against a headwind of competitor incentives and value-reducing fleet sales,” Mendel said in a statement Tuesday.