* Output down 18 pct, sales tumble 25 pct from January due to Carnival
* Output up 5 percent and sales down 6 percent from year-ago
* Weak economy, end of tax breaks lead to dimmer 2013 outlook (Adds details of industry's performance)
SAO PAULO, March 6 (Reuters) - Brazilian auto production and sales tumbled in February, the national automakers' association said on Wednesday, as holidays weighed on the world's fourth-largest car market.
Automobile production in Brazil fell 18 percent and sales dropped 25 percent in February from January, according to data from industry group Anfavea.
Brazil's world-famous Carnival celebrations slow many of its industries to a crawl for nearly a week in February. Compared to a year earlier, output rose 5 percent and sales fell 6 percent.
Weak economic growth and the expiration of tax breaks has led the industry to lower its sights for 2013 after auto output fell last year for the first time in a decade.
Brazilian dealerships lowered their growth forecasts to 3.1 percent for cars and 0.7 percent for light trucks this year, industry association Fenabrave said on Tuesday, down from 3.5 percent and 1.1 percent, respectively, in January.
Brazil is a key market for the world's biggest automakers, including Italy's Fiat SpA, Germany's Volkswagen AG and U.S.-based General Motors Co and Ford Motor Co, which sell about 70 percent of new cars in the country. (Reporting by Alberto Alerigi Jr.; Writing by Brad Haynes; Editing by Gerald E. McCormick and Phil Berlowitz)