March 26 (Bloomberg) -- Enel SpA, Italy's biggest utility, and Acciona SA said they will bid at least 23.4 billion euros ($31.2 billion) for the 54 percent of Spanish power company Endesa SA they don't already control, trumping a bid by E.ON AG.

The price would be a minimum of 41 euros a share, Acciona said today in a statement. E.ON earlier raised its offer to 40 euros a share, the third time it has increased its bid.

Their proposal may prolong the takeover battle for Endesa as Spain's stock market regulator ruled last week that Enel and Acciona can't bid for six months unless E.ON pulls its 42.4 billion-euro offer. Germany's biggest utility said it filed complaints against the two companies with Spanish and U.S. authorities to prevent them from going ahead.

``The fact that they hold almost half of Endesa's stock seems to condemn E.ON's bid to failure,'' said Stefano Perotto, who helps manage about $150 million at Nuovi Investimenti in Biella, Italy. ``However, we've still got a long battle ahead of us because investors have to wait for an Enel-Acciona bid.''

Shares of Endesa jumped 3.7 percent to 40.06 euros in Madrid. Acciona stock was little changed at 162.1 euros, while Enel shares closed at 7.89 euros. E.ON stock fell 0.4 percent to 100.27 euros in Frankfurt.

Greater Competition

Endesa's 22 million customers and hundreds of power plants make the company a prize as the European Union opens the region's energy market to more competition from July 1.

Acciona, a Spanish construction company, and Rome-based Enel would jointly manage the company. Enel owns 10 percent of Endesa and has reserved another 14.98 percent of the stock through investment banks. Acciona owns about 21 percent of Endesa.

The two won't be allowed to bid for Endesa until September, six months after the end of E.ON's tender period. Enel and Acciona said they'll pay interest on the stock they buy to cover the period until the offer is filed.

E.ON asked Spanish regulators to stop its two rivals from buying any more Endesa shares and to force them to sell those they already own. It also plans to file suits against Acciona and Enel in New York for violating U.S. market information rules.

``Any potential offer from Enel and Acciona remains unsure at this point,'' said Theo Kitz, an analyst at Merck Finck & Co. in Munich, who has a ``Buy'' rating on E.ON shares. ``Investors will have to wait at least six months and E.ON has a strong legal case against the two companies.''

Recommends Offer

Endesa's board recommended E.ON's offer to shareholders in a regulatory filing today. Board members said they will sell most of their stock to the German utility.

Caja Madrid, which owns 9.9 percent of Endesa, will support E.ON's bid and agreed to cede control of its stake to the German utility in a so-called equity swap, the Spanish savings bank said today in a statement.

European utility mergers and acquisitions reached a record $250 billion last year as companies scrambled to expand in faster growing markets. All European households will be free to choose their supplier from July, three years after that right was granted to businesses.

Iberdrola SA of Spain agreed to buy Scottish Power Plc for about $23 billion euros, and Gaz de France SA and Suez SA are planning to merge in a transaction valued at about $59 billion.

Nominating CEO

Acciona would control a holding company owning a majority stake of Endesa and would name the power company's chairman under the proposed partnership with Enel, it said in today's statement. Enel would be allowed to nominate the chief executive officer.

E.ON Chief Executive Officer Wulf Bernotat has been seeking to enter territories with faster-growing energy consumption than his home market. German power use in the first three quarters of 2006 increased 0.6 percent from the year-earlier period, according to power industry organization VDEW. In Spain, the gain was 3.3 percent.

Enel CEO Fulvio Conti has set aside at least 15 billion euros for acquisitions and development of plants in areas such as Spain, France, Eastern Europe and the Americas, he said in an interview on Feb. 12. The company, which owns, Spanish power company Viesgo, can also take on debt to fund purchases, Conti said.

Conti has said there will be room only for a few large energy groups in Europe over the next several years, and he wants Enel to be one of them. The company has looked for assets since the French government spurned its planned bid for Suez last year.

To contact the reporters on this story: Anthony DiPaola in Rome at adipaola@bloomberg.net.

Last Updated: March 26, 2007 16:10 EDT