By Bernie Woodall

DETROIT (Reuters) - Automakers in the United States are ramping up holiday sales promotions ahead of Black Friday, aiming to clear out bulging inventories of unsold cars and dispel investor doubts about consumer demand.

Detroit automakers need a strong year-end sales push. They are sitting on hefty inventories of unsold sedans, compact cars and sports cars as consumers shift to pickup trucks and SUVs.

The share prices of General Motors Co <GM.N>, Ford Motor Co <F.N> and Fiat Chrysler Automobiles NV <FCAU.N> <FCHA.MI> are flat to down for the year. This reflects investor concerns that a six-year auto sales boom in the United States is reaching an end and that sustaining sales levels will require more aggressive price cutting.

"We are seeing a tougher pricing environment, higher levels of discounts," said Ford Chief Executive Officer Mark Fields. He predicted November and December sales would be about the same as a year ago, when the annualized sales pace averaged about 17.9 million vehicles a year.

Ford kicked off its Black Friday sales promotions in early November, after reporting an 11.7 percent drop in October sales.

Rivals have since followed suit. GM's GMC truck brand is promoting "Black Friday All Month Long" with discounts of as much as 20 percent off list prices for pickup trucks.

Luxury automakers usually join the fray in December. Toyota Motor Corp's <7203.T> Lexus brand began touting its annual "December to Remember" deals ahead of Thanksgiving weekend, offering 0.9 percent, five-year loans or $1,000 off on its compact IS 300 sedan in certain markets.

GM this week began offering markdowns on the Chevrolet Corvette sports car through retailer Costco Wholesale Corp's <COST.O> car-buying club, the first time the Corvette has been offered through the discount retailer's car buying service.

At the start of the month, there were 122 days of Corvette inventory, up 51 percent from a year earlier and nearly double the level automakers consider ideal, according to Automotive News data.

Like other retailers, automakers use holiday-themed promotions to boost sales during the final two months of the year, and like Wal-Mart Stores Inc <WMT.N>, Target Corp <TGT.N> and Amazon.com Inc <AMZN.O>, automakers have steadily expanded the Christmas season over the past several years.

GOING GLOBAL

The concept of winter holiday sales is going global. Black Friday car deals came to Britain about six years ago. In China, automotive marketers target customers on Singles Day, Nov. 11, led by Alibaba Group Holding <BABA.N>.

Singles Day has become the largest shopping day of the year as Alibaba encourages vendors on its sites to offer heavy discounts on items from cars to clothing.

Automakers in the U.S. market will report November sales on Dec. 1, and analysts expect an increase in total U.S. auto sales from a year ago. The annualized sales pace could drop, however, to 17.9 million vehicles, according to J.D. Power and LMC Automotive. A year ago, the annualized selling rate for November was 18.25 million vehicles, according to Autodata Corp.

A factor working in the automakers' favor is the advanced age, 11.6 years on average, of the U.S. fleet of 264 million vehicles.

It is unclear to what extent automakers will offer deeper discounts overall in the coming weeks or repackage existing deals with holiday bows.

J.D. Power data on new-vehicle discounts provided to Reuters shows that on average GM discounts grew 1 percent in October from a month earlier, to $4,700 per vehicle, while Ford's average discount fell 10.6 percent to about $4,400 per vehicle. Fiat Chrysler's October discounts were flat at $4,920 in October from September, according to J.D. Power. But the company offered $7,800 or more off its top-seller, the Ram 1500 pickup truck.

“Incentive levels are near record highs as a percentage of the selling price," said Jeff Schuster, lead forecaster for LMC Automotive, an automotive consultancy.

At the same time, Detroit automakers are cutting production. Both GM and Ford recently announced production cuts. GM announced indefinite layoffs for 2,000 workers at two U.S. factories that build various car models. Ford ordered temporary layoffs.

For a graphic on U.S. autos days supply, click http://fingfx.thomsonreuters.com/gfx/rngs/USA-HOLIDAYSHOPPING/010030N51EB/USA-HOLIDAYSHOPPING-AUTOS.jpg

(Additional reporting by Alexandria Sage in Los Angeles, Catherine Cadell in Beijing and Costas Pitas in London; Editing by Cynthia Ostermanand Jonathan Oatis)