* Inquiry followed VW Dieselgate scandal
* Concerns several models including Fiat and Alfa Romeo
* Investigators suspect attempt to hinder their work (Adds detail, background)
PARIS, Oct 23 (Reuters) - A French judicial inquiry into Fiat Chrysler over suspected emissions-test cheating centres on whether the carmaker misled buyers of Fiat, Alfa Romeo, Jeep and Lancia cars about emissions levels, according to a letter seen by Reuters.
The letter, dated Oct. 17 and sent by the magistrate leading the investigation to people involved in the probe, also says that French investigators suspect that attempts were made to hinder the work of one of the investigators, an official whose job is to note breaches of France's consumer laws.
Fiat declined to comment on the matter when contacted.
French prosecutors opened a formal investigation into Fiat Chrysler in March over allegations that the carmaker cheated in diesel emission tests.
The precise nature of that inquiry has been vague.
In the letter, the head of the investigation says the suspected emissions cheating dated back to as early as September 2009 and involved brands including Fiat, Alpha Romeo and Jeep but did not say over which period.
The letter says investigators also suspect "obstruction of the work of an official tasked with registering breaches of the consumer code".
Fiat shares were down by around 1 percent in Milan in mid-session trading on Monday.
The inquiry into Fiat Chrysler came in the wake of Volkswagen's diesel emissions-test cheating, exposed by U.S. regulators in 2015 and known as Dieselgate, which triggered dozens more investigations into possible test-rigging by other carmakers.
Dieselgate also prompted a push by some lawmakers to ban diesel engines and eventually all combustion engines.
In May, the U.S. Justice Department sued Fiat Chrysler, accusing the company of illegally using software that led to excess emissions in nearly 104,000 U.S. diesel vehicles sold since 2014. It also faces numerous lawsuits from owners of those vehicles.
The European Union has also launched legal action against Italy for failing to police allegations of emissions-test cheating by Fiat Chrysler properly, following the Volkswagen Dieselgate scandal. (Reporting by Emmanuel Jarry and Agnieszka Flak; Writing by Sudip Kar-Gupta; Editing by Brian Love and Susan Fenton)