DETROIT – Despite the tough American economy, General Motors Corp. has started the year off right – holding its share of the retail market in the first three months with a stable of strong new products such as the Chevy Malibu, Buick Enclave and Cadillac CTS.

GM captured 21.6 percent of retail sales in the U.S. market during the January-March period, according to the latest estimates provided exclusively to the Detroit Free Press by the Power Information Network, a subsidiary of J.D. Power and Associates.

Rivals Chrysler LLC and Ford Motor Co., meanwhile, performed poorly.

Chrysler lost 1.5 percentage points of share, ending with 9.8 percent. Ford dropped a little more than a half percentage point to 13.9 percent. Those are substantial declines when one considers that every percentage point of annual market share is about the equivalent of one assembly plant’s full production for the year.

Retail sales are those made directly to consumers, and they exclude fleet sales to rental car companies, businesses and governments, which are typically sold at a discount. Industry experts view retail sales as one of the best measures of demand and future financial performance because they are generally more profitable.

Automakers release only their overall sales results, which combine retail and fleet performance, so the Power Information Network provides its own estimate of retail-only performance based on transaction data from more than 7,000 dealership franchises.

Japanese automakers, led by Honda Motor Co. and followed by Toyota Motor Corp. – both of which dominate lists of the nation’s most fuel-efficient vehicles – picked up the 2.3 percentage points of retail market that Detroit lost and then some.

In all, Detroit’s automakers now sell just 45.3 percent of the cars and trucks purchased by American consumers in dealer showrooms – a new low.

According to the estimates from Power, Detroit’s automakers have sold less than half of the cars and trucks in America since the second quarter of 2006 and their collective grip on the American consumer has slipped further since then, despite GM’s steady performance.

Among American consumers:

GM is still No. 1, followed by Toyota, which has 18.6 percent of the market.

Ford is No. 3, with Honda advancing quickly, with 12.4 percent of the market.

And Chrysler is No. 5, with Nissan not far behind.

Tom Libby, senior director of industry analysis at the Power Information Network, said Chrysler’s drop was the most concerning among Detroit’s automakers.

Chrysler’s lost share, relative to its size, was the worst performance of any major automaker.

“It’s huge, it’s huge,” Libby said of Chrysler’s declines. He cited a variety of mistakes he believed Chrysler is making in the market, such as losing its focus on the minivans and letting Dodge fall behind its rivals in offering crossovers, coming to market late with the Journey.

“They did not get off to a good start,” Libby said of Chrysler’s new year.

While Libby said Ford’s year-over-year performance is concerning, too, Ford’s retail market share was essentially flat with the last three months of 2007, when the automaker sold 13.8 percent of the new retail cars and trucks in America. That number includes all of the company’s six domestic and foreign brands, as Ford is still in the process of closing the sale of Jaguar and Land Rover.

Libby said he has confidence Ford is making the right moves to improve its share with the Ford and Lincoln brands.

However, he said that Mercury, which has nearly a full percentage point of market share in the United States, has been long neglected and is a source of vulnerability for Ford.

Aside from a hybrid version of the Milan sedan slated for release later this year, Libby said, “we aren’t aware of any new products coming.”

For years, automotive analysts have told the Detroit Free Press that Ford should kill the Mercury brand and divert its marketing and development dollars to the Ford brand, which they say has the potential to rival Toyota.

However, in response to questions about whether Ford was preparing to let Mercury go, Jim Farley, Ford’s group vice president for marketing and communications, has said the company is committed to Mercury, which is situated between the mainstream Ford and upscale Lincoln.

“To be honest, we have some pretty significant product investments in Mercury coming in the second half of the year,” he told journalists this month. “We have a whole new powertrain for Mariner, and we have a significantly revised Milan with a hybrid … We do have a lot of marketing plans for Mercury.”

Among Japanese automakers, Honda turned in the most impressive retail performance of the first quarter.

It added more market share than any other automaker, nearly a full percentage point, on the strength of its fuel-efficient cars, which also have some of the highest resale values in the industry. Honda now sells 12.4 percent of the vehicles in America, with a stable of popular small cars such as the Civic and Fit.

“They are benefiting from their overall image,” Libby said.

Toyota, which has a strong reputation for fuel efficiency, quality and value, delivered a standout performance, gaining nearly a percentage point, too.

Libby said the advance of the Japanese automakers remains the biggest trend in the retail market.

“They just seem to be relentlessly moving forward,” he said.