GM's U.S. sales were down 14.6 percent, it's biggest slide since October, while Ford's overall sales were down 4.6 percent last month, hurt by sluggish sports utility vehicle sales.
The declines at Ford and GM, both of which plan to shutter factories and cut blue-collar workers in sweeping restructuring programs, cast another shadow over Detroit's struggling automakers as they grapple with brutal competition on their home ground.
DaimlerChrysler AG's (DCX) Chrysler unit was the lone Detroit automaker to post a sales rise of 2 percent.
Ford and GM, which lost $10.6 billion last year, have seen a protracted sales decline to more nimble companies such as Japan's Toyota Motor Corp. (TM), which reported its best- ever monthly sales in March.
Toyota said customer purchases rose 6.9 percent last month. Honda Motor Co. Ltd.'ssales were up 0.2 percent, while sales of Hyundai Motor Co.(HMC) Ltd. increased 4.3 percent. Nissan Motor Co. Ltd.'s sales fell 2.6 percent.
Ford's chief sales analyst said the automaker is making progress toward stabilizing its market share.
"We're not there yet, but we are reducing the rate of decline and that's our goal in 2006," said Pipas, who expects Ford's market share in March will be flat to down a little.
"If we look at the first quarter, it would seem as if we have cut the rate of decline in half and that's a good start."
The sales results came as U.S. automakers dialed up their spending on sales incentives last month, according to an industry tracking firm.
SALES OF NEW PRODUCTS UP
Toyota's top U.S. executive, Jim Press, told Reuters in a telephone interview that new vehicles — Rav4 and FJ Cruiser SUVs, redesigned Camry and the new Yaris subcompact car — drove sales gain.
Toyota sold 1,339 Yaris cars in March even though the model made its debut in dealerships only mid-month.
"The initial response to it is much greater than we thought," Press said.
One key for GM is the strength of sales of its 2007 Chevrolet Tahoe and Yukon sport utility vehicles, the first few in a revamped series of large SUVs that are central to the automaker's turnaround strategy.
Tahoe sales were up 41 percent compared with February sales and up 20 percent versus a year ago. Yukon sales were more than double its sales in February, GM said.
In a bright spot for Ford, its trio of new cars that were launched last fall — Fusion, Milan and Zephyr — continued to see strong sales and were up 28 percent in March compared with February.
Sales of Ford's profitable F-Series pickup trucks were up 4.5 percent in March. But sales of Ford's Explorer and Expedition SUVs were down 31 percent and 13 percent, respectively.
A survey released by industry tracking firm Edmunds.com said the average incentive on a vehicle sold in March was $2,510, up 7 percent from February.
Edmunds estimated the industry spent $3.8 billion on incentives in March, with GM and Ford accounting for 71 percent of the total.
The combined incentive spending for Detroit's Big Three automakers averaged $3,205 per vehicle in March, up from $3,001 the previous month.