Despite an assertion by its own public advocate that a sweetheart deal on mass-mailing rates would be overturned by federal courts, the Unites States Postal Service has plunged ahead.

The U.S. Postal Regulatory Commission approved a 20 percent discount on mailings beyond its current volume for Valassis, a huge direct mail company based in Michigan.

It is dubious public policy for the USPS to favor a national company over thousands of small businesses. As Malin Moench, the public advocate, told the commission, the Valassis agreement is "designed to manipulate prices and to alter the balance of market forces."

The commission contended that its decision will survive an anti-trust challenge because the revenue it will produce is above costs.

Mr. Moench said the decision misinterprets antitrust law and predicted that it will be overturned due a newspaper industry appeal in federal court.

The USPS, already bleeding, should not forsake some of its best customers for the sake of another. It's bad policy that should be reversed, whether through the appeal or by the service itself.