CHICAGO (AP) _ Harris Bankcorp and its parent, the Bank of Montreal, have agreed to acquire Suburban Bancorp for about $246 million in the parent company's stock.

The purchase of Palatine-based Suburban surprised many analysts because Suburban is controlled by a single family - led by Chairman Gerald F. Fitzgerald and two of his sons - and most believed they would keep it independent.

''If I had drawn my top 10 list of takeovers, they wouldn't have been on it,'' said Greg Anderson, an analyst at Chicago Corp.

The merger must be approved by regulators and Suburban's shareholders, but the Fitzgerald family already has approved the deal. Chicago-based Harris last year had assets totaling $13.5 billion. Suburban had 1993 assets of $1.3 billion.