GM, the world's largest automaker, said its sales fell 22.2 percent, with trucks falling 31.2 percent and cars inching down 2.7 percent.
At Ford, sales of Ford, Lincoln and Mercury vehicles dropped 35.2 percent from a year earlier as trucks sank 44.8 percent, while cars slipped 6.7 percent. Sales of F-Series pickup trucks, long the country's best-selling vehicle and the company's most important vehicle, skidded 45.6 percent.
Paul Ballew, GM's executive director of global market and industry analysis, said the year-over-year decline was in line with expectations after "inflated" sales in the summer of 2005.
Ford said it was heartened by growing retail demand for its new mid-size sedans, the Ford Fusion, Mercury Milan and Lincoln Zephyr. Retail sales for the vehicles were up 18 percent over June, the company said.
The nation's second-largest automaker said demand for the sedans should remain high, as 2007 models, with additional safety features and optional all-wheel drive, hit showrooms. They went into production Monday.
But Ford's lineup of new vehicles is thin this year compared to its competitors. In the fall, it is scheduled to introduce two crossovers, the Ford Edge and the Lincoln MKX. The company hopes the more fuel-efficient SUV alternatives will help it hold on to market share as high gas prices cause consumer tastes to shift.
"We had a solid retail month in July," Al Giombetti, president of Ford and Lincoln Mercury sales and marketing, said in a statement. "We are particularly encouraged by the response to our new cars, which offer distinctive styling and outstanding fuel economy. They are definitely the right products at the right time."
In the first seven months of the year, Ford's sales fell 9.7 percent, with trucks dropping 17 percent and cars slipping 5.7 percent. GM's sales fell 14.1 percent year to date, with trucks down 16.7 percent and cars off 9.7 percent.
GM shares fell 95 cents, or 3 percent, to $31.28 in afternoon trading on the New York Stock Exchange while shares of Ford fell 9 cents to $6.58.