DETROIT — General Motors’ October U.S. sales plunged 45 percent and Ford’s dropped 30 percent, as low consumer confidence and tight credit combined to scare customers away from showrooms.

The results released Monday — along with drops of at least 23 percent for Toyota, Honda and Nissan — appeared to fulfill prophecies that the industry’s sales as a whole will hit their worst level in decades.

Mike DiGiovanni, General Motors Corp.’s executive director of global market and industry analysis, said the automaker expects last month was the industry’s worst U.S. sales performance since 1975 with only 851,000 vehicles sold, for an annual rate of 10.7 million vehicles.

“This is clearly a severe, severe recession for the U.S. automotive industry and something we really can’t sustain,” DiGiovanni said. “There really needs to be actions focused on the consumer and available credit.”

Other automakers were scheduled to report their sales later Monday.

Detroit-based GM said its light trucks sales tumbled 51 percent compared with the same month last year, while demand for passenger cars fell 34 percent.

The results were less severe at Ford Motor Co., which said its Ford, Lincoln and Mercury car sales were off 27 percent, while light truck sales for the three brands were down more than 30 percent.

Overall, GM sold 168,719 vehicles, while Ford, including its Volvo brand, sold 132,278 light vehicles last month.