Southern National Corp. announced an agreement Monday to acquire United Carolina Bancshares in a pricey transaction that would make it the largest in North Carolina deposits. For $985 million in stock, or 2.85 times book value, Southern National's Branch Banking & Trust Co. would vault past First Union Corp.'s First Union National Bank to become No. 1 in the state that is also home to NationsBank Corp. and Wachovia Corp. Increasing total assets by a pro forma $4.4 billion, to $25.8 billion, Southern National would jump five notches on the U.S. bank holding company list, to No. 30. Analysts said given the banks' high price-earnings multiples and anticipated expense reductions of $65 million, the price was not unreasonable. Said John Bailey, an analyst with Friedman, Billings, Ramsey & Co. in Roslyn, Va.: "Even using a conservative formula for the cost savings they hope to achieve, this looks like a really good deal."