Fiat Chrysler Automobiles, Alfa's current owner, this week revealed a strategy for the sporty Italian brand to race from zero to 150,000 sales in just four years. But industry experts, some citing the more than two decades it took Volkswagen's (>> Volkswagen AG) Audi brand to achieve that market level, say the plan is overly ambitious.

"It is mathematically possible for Alfa to sell 150,000 in North America by 2018, but so is winning the lottery," LMC Automotive analyst Jeff Schuster said.

Chief Executive Sergio Marchionne and his team revealed their strategy for Alfa Romeo on Tuesday as part of a five-year plan to establish Fiat Chrysler as a strong global automaker. But Fiat SpA's (>> Fiat SpA) shares fell so quickly on Wednesday that trading in them was suspended briefly.

Critics of the Alfa rejuvenation plan, including investors, industry analysts and bankers, cite concerns about distribution, the challenge of bringing eight new models to market in such a short time frame and the intense competition of the market.

This is not the first time Marchionne said Alfa was coming to the United States. In January 2013, he said "for sure" it would return that year with the 4C sports coupe. The car is now expected to make it to the U.S. market later this year, followed by a higher-volume model in late 2015.

Industry observers say Marchionne had better have his back-up plan ready.

"One hundred fifty thousand sales; what's Lincoln doing this year? And they're trying," said a banker who asked not to be named, referring to Ford's luxury brand, which sold about 82,000 vehicles last year.

Fiat's plan depends on several elements that leave observers cold, starting with selling Alfa vehicles through Fiat show-rooms.

“Alfa will only work if it’s got a dedicated facility or it is paired with another luxury brand,” said Jim Ziegler, a U.S. auto dealer consultant. “You can’t have the same sales team selling $17,000(10,088 pounds) cars from one brand and $60,000 cars from another. It just doesn’t work that way.”

Fiat Chrysler is expected to sell Alfas at its best-performing Fiat dealers, as well as high-end Maserati dealers. Fiat dealers number 344 in North America, while Maserati locations total 91.

Harold Wester, CEO for Alfa and Maserati, raised eyebrows when he said eight new Alfa models would be introduced from late 2015 through 2018.

"They've got to develop in the space of four years an entire portfolio of vehicles," AutoTrends analyst Joseph Phillippi said. "That's a huge engineering challenge."

While the U.S. luxury market is growing, the competition is fierce. Mirko Mikelic, senior portfolio manager for Clear Arc Capital, said it is hard to believe Alfa Romeo "will come in and start muscling out" rivals.

Among them are well-established brands such as Daimler's (>> Daimler AG) Mercedes-Benz and BMW (>> Bayerische Motoren Werke AG), which are only making it tougher for competitors as they push down market to vehicles starting as low as $30,000, analysts and bankers say.

Alfa's planned North American return after leaving in 1996 was preceded by the re-introduction of Fiat in 2011. However, sales of the subcompact Fiat 500 have disappointed and Fiat dealers are struggling with only two models to sell. Fiat sales in the United States and Canada were about 51,000 last year.

In acknowledging that the company's overall plan for the 2014 to 2018 period is aggressive, Marchionne said he understood Wednesday's nearly 12 percent drop in the stock price. “We’ve had a phenomenal run in 2014 ... and I am not surprised that people took some money off the table,” he said.

Marchionne also said he can "pull the plug" on the plan to invest 5 billion euros ($7 billion) to remake Alfa.

That did not make investors feel any better about an overall plan that includes the goal of boosting annual global sales by about 60 percent from 2013 to 7 million vehicles.

Fiat Chrysler also intends to boost its U.S. market share to 15.8 percent from 11.4 percent last year. That would position it for second place, and analysts and bankers say Ford Motor Co (>> Ford Motor Company) and Toyota Motor Corp (>> Toyota Motor Corp) will not let anyone pass them without a fight.

Even believers know they are taking a chance. "Whoever bets on Fiat today, bets on a possibility, on a potential," said Roberto Lottici, fund manager at Ifigest.

(Additional reporting by Ben Klayman and Agnieszka Flak in Detroit; Editing by Dan Grebler)

By Bernie Woodall