PacifiCorp, the Portland, Ore.-based utility giant, today increased to $1.82 billion its offer to acquire Arizona's largest utility, Pinnacle West Capital Corp. PacificCorp also agreed to assume all of the debt of Pinnacle West and its subsidiary Arizona Public Service Co. as part of the offer. Steve Carr, a Pinnacle West spokesman, said the company's board of directors would ``seriously consider'' the offer. Pinnacle West's board rejected three previous offers from PacifiCorp.The last offer, worth about $1.7 billion, was rejected in March as inadequate. Under the new offer, Pinnacle West shareholders would received $21 in cash for each share of stock they hold at the time of the acquisition. Pinnacle West stock sold for $12.75 at the close of trading Wednesday. ``We think it is time to bring to a conclusion PacifiCorp's expressions of interest to you ...,'' PacifiCorp President and Chief Executive Officer A.M. Gleason said in a letter delivered Thursday to Richard Snell, chairman of Pinnacle West. ``Our offer remains the same with regard to customers of Arizona Public Service: Rate increases limited to 2 percent per year for four years. ``This is significantly less than the rate relief requested in APS's most recent filing with the Arizona Corporation Commission: Rate increases of 6.5 percent per year for three years.'' PacifiCorp has said it wants the Arizona utility so that it could conduct seasonal transfers of excess power between Arizona, where power use peaks in the summer, and the Pacific Northwest, where power use peaks in the winter. Gleason said the deal would delay into the next decade any need for PacifiCorp to build additional power plants to meet peak demands. PacifiCorp has electric utility operations in seven Western states. Prior to receiving the offer Snell was not enthusiastic about a deal. ``If there's another offer, we'll take a look at it,'' Snell said. ``But our position is that this is not a good time to sell, and the company is not for sale. ``On the other hand, we've given serious consideration to the other offers, and we will again if one comes our way.''