U.S. auto sales lost momentum in the final weeks of January, auto executives and a leading analyst cautioned on Monday, setting the stage for a softer start to 2011 than the industry had expected.

J.D. Power, which gathers sales data from almost 9,000 U.S. car dealerships, issued an unusual update to its monthly sales forecast on the eve of the Tuesday sales report, cautioning that consumers had pulled back from purchases ahead of the crucial end of the month.

Both Ford Motor Co and Chrysler Group LLC also suggested industry-wide sales could fall short of the most bullish forecasts.

U.S. auto sales represent one of the first snapshots of consumer demand. A result at the low end of expectations could raise new caution at a time when some analysts have tamped down bullish expectations for the speed of the earnings growth for U.S. automakers and suppliers in 2011.

The strength of retail sales from the beginning of the month has reversed during the past two weeks, said Jeff Schuster, J.D. Power's chief forecaster.

Schuster said the sudden slowdown in sales in January could reflect both the impact in winter storms and the absence of new sales incentives from major automakers. Those kinds of discounts, including cash-back offers, were down 12 percent in January from December, he said.

J.D. Power forecast a January sales rate of between 11.5 million and 12 million vehicles, down sharply from the outlook for 12.2 million it had given just 10 days before.

Automakers are set to report January U.S. auto sales on Tuesday.

Economists surveyed by Reuters had forecast sales for the month of about 12.5 million vehicles on the annualized and seasonally adjusted basis tracked by the industry.

That would be slightly higher than the 12.4 million sales rate that the industry averaged in the fourth quarter. It would also represent the best January sales result since 2008.

Of the 14 analysts surveyed by Reuters, forecasts ranged from a low of 12.1 million to a high of 13 million.

CHRYSLER, FORD CAUTIOUS

But on Monday Chrysler Chief Executive Sergio Marchionne said that industry-wide sales had fallen off in the final weeks of the month, which typically account for the bulk of sales.

We've seen a softening of the U.S. market in the last couple of weeks, Marchionne told reporters on a conference call to discuss Chrysler's fourth-quarter results.

Marchionne forecast a sales rate of near 12.4 million to 12.5 million vehicles for the month. Chrysler is 25 percent owned by Italy's Fiat SpA.

Ford also said industry-wide sales would point toward a continued, gradual recovery but offered up an estimate for the tally that fell short of the most optimistic projections.

It's probably too much to expect that sales go up and up and up without interruption, Ford's chief sales analyst, George Pipas, told reporters. These things just don't happen.

Pipas said Ford expected industry-wide sales for the month would be near 800,000, up from 700,000 a year earlier,

That gain would translate into an annualized sales rate near 12.3 million vehicles, down from 12.6 million in December.

Winter storms pummeled much of the United States in January, snarling showroom traffic in parts of the country that are normally outside the Snowbelt.

That included a particularly strong winter storm in the middle of January that caused six states to declare states of emergency, shut interstate highways around Atlanta and dropped heavy snow in parts of Texas and the Carolinas.

The weather was a new factor for us but our sales were up, said Mark Whibbs, a Buick and GMC dealer in Pensacola, Florida.

One of the keys for January will be the extent of the sales rebound for Toyota. <7203.T>

In January 2010, Toyota had been rocked by a massive recall and a sales shutdown on eight of its 19 U.S. models due to faulty accelerator pedals.

Toyota has forecast a double-digit percentage sales gain in 2011 sales, outpacing the industry.

TrueCar.com, one of the few industry-tracking firms to offer a company-specific sales forecast, projected a 29 percent sales gain for Toyota in January, the largest rise for any of the major automakers.

(Reporting by Kevin Krolicki and Bernie Woodall, editing by Matthew Lewis

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