AT&T; and Quotron will build a computer system.

The computer-based financial information system that AT&T; and Quotron have agreed in principal to develop and sell will be designed for stockbrokers and securities analysts. A broker using the system will be able to do several things simultaneously, such as hold a telephone conversation with a customer, view market prices and enter customer orders. Shearson Lehman Bros. will be the first customer, the two companies said.