MADRID (Reuters) - Spain's Banco Popular (>> Banco Popular Espanol SA) offered a steeper-than-expected discount on a 2.5-billion-euro ($3.2 billion) new share issue in a last-ditch attempt to avoid the need for European aid to shore up its finances.

Popular, the country's sixth-biggest bank, unveiled plans for the share issue after an independent stress test of Spain's financial system, published in September, showed it needed an extra 3.2 billion euros to weather a serious economic downturn.

The bank, which like its domestic peers is saddled with bad debts after a burst property bubble, was the largest non-nationalized Spanish entity to fail the stress test.

Popular is offering three new shares for every old one at a price of 0.401 euros each. This represents a 64 percent discount to Friday's closing share price of 1.118 euros, much steeper than the 50 percent discount flagged by the bank in October.

It is 76 percent discount to the 1.701 euros the shares closed on September 28 when the Oliver Wyman audit revealed the capital shortfall at Popular, prompting its plans for a rights issue.

"Despite increased uncertainty in the next two years and very high economic risks, the most sensible option for this bank is to continue its current business model," Popular Chairman Angel Ron said on Saturday while seeking shareholder approval for the plan.

The bank said 15 institutions had underwritten the capital increase with commitments of 2.08 billion euros. Core shareholders like German insurer Allianz (>> Allianz SE) had already said they would support the issue. ($1 = 0.7868 euros)

(Reporting By Tomas Gonzalez; Writing by Tracy Rucinski; Editing by Toby Chopra)

By Tomás Cobos

Stocks treated in this article : Allianz SE, Banco Popular Espanol SA