PORTLAND, Maine -- The Spanish power company Iberdrola SA plans to buy regional utility owner Energy East Corp. for $4.5 billion in cash, giving it a foothold in the United States, the companies said yesterday.  

The boards of both utilities agreed to a deal that would give Energy East shareholders $28.50 per share, a 27 percent premium over Energy East's closing stock price Friday.

The deal is of special interest in Maine, where 80 percent of electric customers are served by Central Maine Power Co., an Energy East subsidiary.

Its subsidiaries would continue to operate under their current names. The others are Berkshire Gas, Connecticut Natural Gas, New York State Electric & Gas, Rochester Gas and Electric, and Southern Connecticut Gas.

The deal, which is expected to close next year, needs approval of Energy East shareholders, the Federal Energy Regulatory Commission, and state agencies.