DETROIT — Ford’s U.S. sales plummeted 21 percent in September while Chrysler and Toyota posted slimmer declines and General Motors held steady. Despite a 4 percent decline in September, Toyota’s sales lead over Ford widened for the year.

General Motors Corp. said Tuesday its sales were flat compared with last September. The company got a boost from its new lineup of pickups as well as the new Cadillac CTS, which posted a 73 percent sales increase.

Honda Motor Co.’s U.S. sales rose more than 9 percent, while Nissan Motor Co.’s sales gained 7 percent on strength of record Altima sedan sales.

But Chrysler LLC said its U.S. sales fell 5 percent, although retail sales were up and fleet sales were down compared with the same month last year.

Ford Motor Co.’s car sales dropped 39 percent compared with last September, while its truck sales were down 5 percent. Sales of Ford’s F-150 pickup, long the best-selling vehicle in the United States, fell 21 percent as newer pickups from GM and Toyota Motor Corp. stole its thunder.

Ford said a 62 percent reduction in sales to rental car fleets partly was to blame. Ford has been trying to cut back on rental sales, which can hurt brand image and profits.

Ford’s overall sales were down 13 percent for the first nine months of the year. Ford hasn’t seen a month when sales rose since October 2006, according to Ward’s AutoInfoBank.

George Pipas, Ford’s top sales analyst, said Ford is on track to cut sales to daily rental fleets by more than its original goal of 30 percent this year, or 135,000 vehicles.

“At the very beginning of the year, we said planned reductions in daily rental were of such a magnitude that we expected a sales decline every month this year,” Pipas said in a conference call with investors and media. “What has transpired has been in line with what our expectations were at the beginning of the year.”

Toyota’s September sales decline was led by its trucks, which were off 5.7 percent. Car sales were down 3.5 percent versus a best-ever September 2006.

Toyota outpaced Ford for the month and for the first nine months of the year, continuing its drive to replace Ford as the nation’s No. 2 automaker in sales after GM. Toyota had sold 28,654 more vehicles than Ford as of the end of September.

GM saw its car sales drop 4.4 percent, but its truck sales were up 3.6 percent. But Chrysler experienced the opposite with car sales up 18.8 percent and trucks down 11.4.

Honda bucked the negative trend thanks to a 7.2 percent rise in car sales, while truck sales were up 12.5 percent. Honda Motor, which includes Honda and the Acura luxury brand, said its Honda division reported a record September. Its new Accord sedan and CR-V crossover vehicle helped fuel the increase, the company said.

Many analysts predicted that jittery consumers put off big-ticket purchases in reaction to the credit crunch, high gas prices and the troubled housing market.