After more than a year of investigations that saw its vice chairman sentenced to prison and its past chairman resign under fire, the Board of Governors of the Postal Service has adopted a code of ethics.

Government rules of ethics have always been applicable to board members, explained Postal Service General Counsel Louis A. Cox, but the vote Tuesday created a formal set of rules specifically for the agency.

The Postal Service has been caught up in a purchasing scandal for more than 14 months. An investigation by the Justice Department and Postal Inspection Service continues.

During that probe, officials have discovered that no formal code of ethics had been written for the governors, the board in charge of operating the massive quasi-independent agency.

The code, approved unanimously, calls on board members to put moral principles and loyalty to country ahead of friends or party, to carry out their duties efficiently, never to discriminate, to engage in no business with the government, to expose corruption when discovered and to avoid conflicts of interest.

The adoption of such rules normally would attract little interest, except that it comes after problems surrounding the purchasing of automated mail-sorting equipment.

Peter E. Voss, former vice chairman of the board, and John Gnau, a public relations executive, have been sentenced to jail in the case.

In May, board Chairman John R. McKean resigned after the Office of Government Ethics found that he appeared to have used his position to benefit a client of his accounting firm in another postal contract matter.

The focus of the investigations has been a $250 million contract for mail-sorting equipment, which Voss was accused of trying to steer to Recognition Equipment Inc. of Irving, Tex. Voss pleaded guilty to accepting an illegal gratuity as part of that effort.

Gnau and Michael Marcus, both of a Michigan public-relations firm working for REI, pleaded guilty to felonies in connection with payments to Voss. Marcus faces six months in a halfway house. No one at REI has been charged with any crimes.