The rating on Watertown, Mass.' bonds reflects: * A sound economic base in close proximity to Boston, * A trend of sound financial performance, and * A moderate debt level. Watertown is a community of 31,000 that borders Boston, with a base primarily oriented toward retail and manufacturing. The Arsenal Mall, a center with 1,174 jobs, and Watertown Mall, a complex employing 500, are the top employers. It is on the strength of these two retail centers that the town had per capita retail sales at 154% of the state and 152% of the nation. Industrial employers include Boston Scientific, a manufacturer of precision tools and instruments with a pay roll of 1,100; and General Scanning, which employs 480. Unemployment