The U.S. Postal Service announced last week a new incentive for postal carriers to buckle up before starting the swift completion of their appointed rounds.

Postal officials said that the service will pay $10,000 to the estate of any of its more than 250,000 drivers nationwide who is killed in an on-the-job accident while wearing a seat belt.

Letter carriers are required to wear safety belts, but Postal Service statistics show that only75 percent of them do. Agency spokeswoman Jeanne O'Neill said a check of 19 recent auto fatalities of postal drivers showed that 18 were not wearing seat belts.

"We thought that was a very persuasive reason for the policy," O'Neill said.

Letter carriers log an estimated 1.5 billion miles a year, she said, and car wrecks kill an average of 12 of them and seriously injure 1,500. The new policy is modeled after a two-year-old General Motors Corp. program to promote the use of seat belts.

Since April 1984, GM has offered a free, one-year insurance policy to buyers of General Motors vehicles that pays $10,000 if the driver is killed while wearing a seat belt. The auto giant has paid 240 such death claims.

GM spokesman Harold Jackson said the company believes its free policies have saved 200 lives and prevented thousands of injuries.

Frank Conners, spokesman for the 275,000-member National Association of Letter Carriers, said the union supports seat-belt use, although he conceded there has been grumbling from carriers whose routes involve constantly getting in and out of vehicles.