Bank of the West said it made a cash offer to buy Westamerica Bancorp. for $100 million, or $18.375 per Westamerica share. The bidder, a San Francisco-based unit of Banque Nationale de Paris, said it sent a letter to Westamerica's board outlining the proposed transaction and requesting a reply by Feb. 10. Joseph Bowler, senior vice president and treasurer of Westamerica, said he was unaware of the overture and had no immediate comment. Bank of the West has assets of $1.5 billion, while Westamerica's assets total $1.25 billion.