UPDATE 2-Brazil's BNDESPar boosts stake in Eletrobras

* BNDESPar buys Eletrobras common, preferred stock

* Eletrobras has been seeking funds for investment

* BNDESPar pledges no change in Eletrobras' structure (Adds Eletrobras CFO comments, updates byline)

By Guillermo Parra-Bernal and Denise Luna

SAO PAULO, Oct. 5 (Reuters) - Brazil's state development bank disclosed on Monday that it boosted its stake in government-run power holding company Eletrobras (ELET3.SA)(ELET6.SA) last month, a move that should help the utility gain financial muscle for investment.

Rio de Janeiro-based BNDES, through its investment holding unit BNDESPar, raised its stake in Eletrobras to the equivalent of 21.1 percent of voting shares and 8.2 percent of non-voting shares from 14.78 percent and 0.44 percent respectively, it said in a regulatory filing dated Sept. 16.

BNDESPar bought the stock from the federal government, the controlling shareholder of Eletrobras.

Terms of the transaction including the price per share and the size of the deal were not disclosed in the filing.

Eletrobras, also based in Rio de Janeiro, is scouring for funds to finance a 30 billion real ($17 billion) investment plan for 2009-2012.

BNDESPar said in the filing the decision "isn't aimed at altering the control of the company or its administrative structure."

Eletrobras Chief Financial Officer Astrogildo Quental said the purchase by BNDESPar might be more related to a strategic investment opportunity rather than a move by the government to boost the company's finances.

"They probably thought that the stock price was very attractive," Quental said from New York. "Soon they might sell it to book profits."

Common shares of Eletrobras slipped 0.2 percent to 27.34 reais in early trading. The preferred stock fell 0.2 percent to 24.64 reais.

Quental said the transaction had nothing to do with a plan by the power utility to pay stock dividends that remain in arrears since 1979-1980.

Eletrobras and its subsidiaries control about 36 percent of power generation and about 60 percent of the transmission grid in Brazil.

Eletrobras is boosting capital spending as President Luiz Inacio Lula da Silva's government uses state companies to mitigate the impact of Brazil's first recession in two decades.

Eletrobras will fund around a third of its investment plan with its own cash resources, which stood at about 13 billion reais at the end of last year. The company was looking to obtain the balance with additional debt and capital injections, according to a report by Fitch Ratings published on July 13.

Executives at BNDESPar and its parent company BNDES could not immediately be reached to comment on the filing. (Additional reporting by Cesar Bianconi in Sao Paulo; Editing by Gerald E. McCormick and Derek Caney)