* Administrator say no valid offers for plant
* Bidders have until April 16 to submit bids
* Plant will close by them if no bids received
By Michel Rose and Muriel Boselli
PARIS, Feb 6 (Reuters) - France's troubled Petroplus refinery in Normandy will close on April 16 unless potential bidders put a valid offer on the table, the legal administrator said on Wednesday, adding no such offer had yet been submitted.
"The bidding deadline was Feb. 5 but the plant's activity will continue until April 16, which is when it will close down if no bidders file an offer in between time," a spokeswoman for the administrator said.
Up until Tuesday, bidders could approach Petroplus Raffinage Petit-Couronne SAS, the administrator for the plant, but from Wednesday until the final deadline any bid would now have to be submitted to the Rouen commercial court.
France's Industry Minister Arnaud Montebourg said on Tuesday authorities had received five bids for the Petit-Couronne refinery, two of them he called "serious."
On Wednesday the administrator identified Switzerland's Terrae International, Lybia's Murzuk Oil, Egypt's Arabiyya Lel Istithmaraat, Cyprus' FJ Energy Group and France's Damanapol International, as interested.
But the firms have not filed offers, they have just expressed their interest, the administrator said.
"We have not put forward a bid yet. We are studying the project and based on the results of our study, we will either offer a bid or not," an Arabiyya Lel Istithmaraat spokesman told Reuters from Cairo.
The French oil industry had greeted with scepticism the news that low-profile, last-minute bidders had put themselves forward to take over the plant.
"Our preoccupation is to obtain assurances on the project's solidity," Jean-Louis Schilansky, the head of French oil lobby UFIP told reporters earlier on Wednesday.
"It would be an absolute catastrophe if there were a buyer which is not solid and serious enough, and that after a few months we end up in a shutdown situation again," he said.
But a consultant who says he has been mandated by the Egyptian company in France, Michel Billard de la Motte, told Europe 1 radio on Wednesday it was ready to invest more than 100 million euros ($135.29 million) in the refinery and maintain all 470 jobs apart from 60 people able to retire.
The group, which said its president would travel to France on Thursday, did not confirm whether Billard de la Motte was its go-between.
"We are present in 10 Middle-Eastern and North African countries, we produce the equivalent of 20 French nuclear plants in terms of electricity," the consultant said.
The Swiss company, Terrae, established in 1984, has no website, but the local commercial registry in that country describes its activities as "all work, studies, research and accomplishment urban centres in Switzerland and abroad."
BIG OIL STAYS AWAY
Big oil firms have shown no interest in the refinery, France's oldest, as oil demand in Europe has dropped sharply and the industry struggles with overcapacity.
If no bids appear to offer the sufficient financial and technical guarantees, the court handling the sale process could decide to liquidate the plant leading to job losses, an outcome the government hopes to prevent.
Socialist President Francois Hollande 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.
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.
Europe will suffer from 8 to 10 percent of overcapacity by 2015 if oil demand continues to fall by 1.5 percent per year, said Schilansky from the Paris-based UFIP which represents companies such as Total, Europe's largest refiner.