General Motors Corp. and Ford Motor Co. will probably say December auto sales in America fell as consumers reined in spending, ending a year with the lowest demand for cars and trucks in a decade.

Deliveries dropped about 5.6% at GM, 7.8% at Ford, and 7.9% at Chrysler LLC, based on the average estimates of six analysts in a Bloomberg survey before tomorrow’s reports. Smaller declines at Japanese rivals such as Toyota Motor Corp., which bumped Ford from the No. 2 spot at midyear, may help them gain market share over Detroit’s money-losing trio. Americans bought about 16.1 million cars and trucks for the year, the least since 1998, with year-end gasoline prices exceeding $3 a gallon for the first time and consumer confidence at a two-year low. Housing starts, one barometer for sales of profitable pickup trucks, are in the deepest slump in 16 years.

“The housing market and credit crunch are really affecting consumers,” an equity analyst with Standard & Poor’s, Efraim Levy, said.

All three of Japan’s biggest automakers will probably report declines for December while collectively gaining market share, an analyst with Edmunds.com in Santa Monica, Calif., Jesse Toprak, said. He predicts declines of 2.9% for Toyota, 0.8% at Nissan Motor Co., and 1.4% for Honda Motor Co.