In an effort to increase its presence in the Washington and Northern Virginia markets, Baltimore-based Mercantile Bankshares Corp. will acquire James Monroe Bancorp Inc. in a transaction valued at about $142.9 million in stocks and cash.

The acquisition of Monroe will add $530 million in total assets, $378 million in gross loans, $471 million in total deposits, and six full-service branches and a loan production office in the affluent markets of Northern Virginia and suburban Washington.