A total of 162,411 new cars were registered last month in France, a statement said, as the French economy, the second biggest in the eurozone, struggled to make headway.
French car makers were among those that suffered the biggest drops, with sales by PSA Peugeot Citroen, the second-biggest European auto manufacturer, down by 5.0 percent, and those by the Renault group posting a plunge of 26.4 percent.
Foreign brands fared better, gaining 2.5 percent overall, with Toyoto, Hundayai-Kia and Daimler, which owns Mercedes-Benz and Smart, leading the way.
Volkswagen, the biggest European car maker, also recorded a gain.
The CCFA expects a drop in car sales of 12 percent for 2012 as a whole, and a spokesman told AFP: "We hope that our forecast is not too optimistic."
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The launch of Renault's Clio IV model, a small car that is well suited to French tastes, could boost end-of-year sales, the spokesman said.