* Some 500 jobs at risk, test for French president
* Deadline for offers on Tuesday at 1600 GMT
* Decision by court not before Thursday
By Michel Rose
PARIS, Feb 5 (Reuters) - Potential bidders for Normandy-based oil refinery Petit-Couronne have until Tuesday to submit offers to legal administrators and avert a liquidation the French government has been desperate to prevent.
Big names in the oil industry have so far shown no interest in the former Petroplus refinery, France's oldest, as oil demand in Europe has dropped sharply and the industry struggles with overcapacity.
The only known firm bidder for the 161,000 barrels-per-day Petit-Couronne refinery so far is NetOil, led by Middle Eastern businessman Roger Tamraz, who submitted an improved offer after the commercial court in Rouen in northern France rejected its initial bid on financial and technical grounds last year.
Other potential bidders have yet to submit firm offers. France's industry minister Arnaud Montebourg sought to strike a deal with the Libyan sovereign fund in November, but the Libyans said they had only sent a letter of intent and it remains unclear whether they are still in the race.
The government has also ruled out a possible offer by Iranian firm Tadbir Energy because of international sanctions banning oil imports from Iran.
"The government did everything to rule out the Iranian offer, even though it wasn't in contravention of the embargo," union representative Yvon Scornet said in a statement.
The Petit-Couronne unions met with government advisers on Monday evening to discuss offers on the table, but have warned of possible industrial action if the plant were to be liquidated.
"If tomorrow a solution is not found, the workers of Petroplus will strike another tone," Scornet said.
But a government source said after the meeting that "chances for a successful outcome were limited".
The Rouen court is expected to rule on the suitability of potential bidders by Thursday at the earliest, after legal administrators have submitted any firm offers to the court. If no suitable buyer appears, the court could decide to liquidate the plant, which would lead of the loss of 500 jobs.
The Petroplus case is the latest stumbling block for Socialist President Francois Hollande, who has vowed to stem rising unemployment by the end of the year but has had to deal with a series of high-profile plant closures.
It is also a test for Hollande's communication skills after his government faced sharp criticism over its mixed messages about a possible nationalisation during a two-month battle over the future of ArcelorMittal's Florange steel plant.
Hollande has said the state could at some point provide financing for the Petroplus facility, but would not take over the plant.
A Petit-Couronne liquidation could also be a headache for former owner Shell, with unions saying the oil major should be asked to contribute to the cost of dismantling and depolluting the site if no buyer was found.
Shell, which operated the refinery since it was opened in 1929, sold the plant to Swiss refiner Petroplus in April 2008, before Petroplus filed for bankruptcy in January last year.
In December, Shell ended a six-month oil processing deal with the troubled plant and has not extended the contract, making the refinery less attractive for buyers due to expensive restart costs.