The consortium, including Italian steelmakers Arvedi and Marcegaglia, submitted the higher bid last week - because Outokumpu sees all bids so far as too low - and it is valid until Friday, two sources with knowledge of the situation said.

Finland's Outokumpu agreed to sell the Acciai Speciali Terni plant more than a year ago to gain approval for its purchase of ThyssenKrupp's Inoxum unit.

The plant - considered one of Europe's most advanced stainless steel mills - is of strategic importance due to its vicinity to steel buyers in Italy, a major steel market, but its profitability has been hard hit by a slump in the steel market.

Loss-making Outokumpu faces a massive writedown on Terni, which is valued at more than 560 million euros ($750 million) on its book but is expected to sell for a fraction of that.

"For Outokumpu all that matters at the moment is getting their debt down but the sale of this plant now will not strengthen their balance sheet considerably. If it strengthens it somewhat they are already lucky," an industry expert said.

"But that plant is a champ in the strategic Italian market and Aperam could get it for a very attractive price."

Besides the Aperam consortium, other parties interested in the plant are Taiwanese steelmaker Yieh United Steel Corp (YUSCO) and U.S. private equity funds Apollo and JPMorgan's One Equity Partners.

Outokumpu said it hopes to complete the sale this year but declined to comment further. Aperam, spun off by ArcelorMittal in 2011 with the Mittal family retaining the biggest stake, said it was still interested in the plant but did not give any further details.

In an attempt to improve its finances, Outokumpu has also been in talks to sell its high-performance alloy unit VDM, for which bids are also much lower than expected.

HARD TO SAY GOODBYE

Outokumpu has twice asked the EU regulator, the European Commission, to postpone the deadline for selling Terni because it sees all the bids submitted so far as unsatisfactory.

Last month the Finnish producer also tried, without success, to persuade the EU to let it keep the Terni mill, pledging worsening market conditions meant it was no longer anti-competitive to keep it.

Terni, about 100 km (62 miles) north of Rome, is a major employer in Italy's Umbria region.

Workers expressed concern at the lengthening sale process and at prospects of job cuts after the sale.

"There is a certain state of resignation here in Terni. We have no idea what lies ahead for us," a worker who has been employed by the plant for more than a decade said.

"There are doubts about Aperam's financial strength and concerns regarding the fact that the Mittal family has proved it has no scruples idling plants. On the other hand private equity is a scary option: they could break up the plant and sell the pieces," the worker said.

Luxembourg-based Aperam announced its ninth consecutive quarterly net loss in the third quarter.

To battle excess supply and slow demand ArcelorMittal, idled two blast furnaces in France last year and has temporarily shut down other plants.

(Additional reporting by Maytaal Angel in London, Arno Schuetze in Frankfurt and Ritsuko Ando in Helsinki; Editing by Louise Ireland)

By Silvia Antonioli