Top automakers reported mixed September sales results on Tuesday, as consumer demand cooled slightly.

Ford Motor Co and Chrysler Group LLC beat analysts' expectations, while General Motors Co , Toyota Motor Corp <7203.T> and Nissan Motor Co <7201.T> fell short.

Ford's sales rose 5.8 percent to 185,146 vehicles, its best September in seven years. Chrysler, an affiliate of Italy's Fiat SpA , said sales were up 1 percent at 143,017, its best September in six years.

Analysts surveyed by Reuters had expected September sales to

decline at both companies.

GM said September sales were down 11.0 percent to 187,197 vehicles. Toyota's sales dropped 4.3 percent to 164,457, and Nissan's fell 5.5 percent to 86,868. All three companies missed analysts' expectations.

Volkswagen AG's U.S. subsidiary said VW brand sales in September fell 12.2 percent to 31,920, while Audi sales rose 6.2 percent to 13,065.

Hyundai Motor Co <005380.KS> said U.S. sales were down 8 percent at 55,102.

The U.S. auto industry's sizzling summer sales pace slowed last month, for what is likely to be the first year-on-year sales decline in more than two years. There were two fewer shopping days in September, compared with the previous year, and part of the Labor Day shopping weekend fell in August.

A federal government shutdown on Tuesday also raised some concerns about consumer demand in October.

A prolonged shutdown could hit new-vehicle sales, said Mark McNabb, chief operating officer at Volkswagen of America.

"There are roughly 800,000 (federal) government workers that could be furloughed, so at some point in time it will have an impact," he told reporters on a conference call.

McNabb said that dealers in the Washington, D.C. area saw a noticeable drop in weekend customers.

Ford Chief Economist Jenny Lin said it was "too early to tell" whether a government shutdown will affect October new-vehicle sales.

INDUSTRY MOMENTUM

Sales of full-size pickup trucks, seen as a bellwether for the U.S. economy, were mixed in September. Ford's best-selling F-Series rose 9.8 percent and Chrysler's Ram was up 8.4 percent, while GM's Chevrolet Silverado, which was redesigned earlier this year, fell 10.8 percent.

Sales by brand, even at Ford and Chrysler, were mixed.

Chrysler's Dodge, Chrysler and Ram brands all reported modest increases in September.

Jeep sales fell 5 percent as Chrysler struggled to get the all-new 2014 Cherokee to dealers. Fiat brand sales plunged 24 percent, the first year-to-year decline in 18 months.

Sales of Ford brand vehicles rose 6.3 percent, while Lincoln sales fell 5.1 percent.

Ford said it posted the best September sales since 2006. Chrysler's September sales were its best since 2007.

Analysts who closely watch the auto industry predict September's annualized sales rate will be in the range of 15.2 million to 15.7 million vehicles. The lower end of that range would fall short of summer's torrid pace, including a 16 million rate in August that marked the strongest performance in nearly six years.

Despite September's expected sales decline of 2 to 5 percent, analysts expect the industry's momentum - it has largely outperformed the broader economy - to continue in the fourth quarter and into 2014 as the factors driving demand remain in place.

"Consumer confidence is relatively high, unemployment ticked down to 7.3 percent in August, and we continue to see increases in home prices and construction activity," Jefferies analyst Elaine Kwei said in a research note.

Barclays analyst Brian Johnson called the expected September sales decline "nothing more than noise."

Average transaction prices for new cars and trucks continued to rise, hitting a record $31,854 in September, according to researcher TrueCar. Prices rose $602 from August as automakers sent more 2014 models to dealers and reduced incentives on leftover 2013 models, TrueCar said.

Chrysler projected the industry's annualized rate in September at 15.7 million vehicles, including about 300,000 heavy trucks.

GM said industry sales hit an annual rate of 15.3 million in September, off slightly from the 15.5-million pace for the first nine months.

GM shares were down 0.3 percent at $35.86 and Ford shares were up 2.2 percent at $17.24 on Tuesday morning on the New York Stock Exchange.

(Editing by Gerald E. McCormick, Maureen Bavdek and Matthew Lewis)