An article yesterday misstated the value of commercial airlines' contracts to carry U.S. Postal Service freight. Airlines earn about $10 billion a year from all types of businesses that use commercial passenger planes to transport freight, of which $1 billion is Postal Service business. (Published 2/1/91)

The U.S. Postal Service yesterday stopped its practice of shipping millions of packages across the country on commercial passenger airlines because of increased concerns about terrorism, according to the airline industry.

The Postal Service has told airlines that any parcel heavier than 16 ounces that is not screened by airport security procedures will not be loaded on passenger planes, said William E. Jackman, spokesman for the Air Transport Association.

Under normal circumstances, packages are "not screened unless for cause," Jackman said. The airlines "are taking a look at whether they can handle screening the stuff" with existing security equipment or whether the Postal Service should be required to screen the parcels before they are loaded.

The packages that ordinarily would be sent in the luggage compartment of passenger planes will, as of yesterday, be flown on contracted cargo planes or transported by truck.

The Postal Service refused to discuss the new procedure yesterday, citing security.

Officials would not comment on the cost of switching some parcel mail from passenger carriers to cargo planes and ground transport, nor would they say how many parcels are shipped by passenger plane each year or whether the delivery time of its overnight mail would be affected.

But Postal Service spokesman Robert Becker insisted that any new changes will not affect delivery schedules.

About 250,000 pounds of mail of all types arrives on planes landing at National Airport each day, postal officials told The Washington Post in 1988. Another 300,000 pounds flies out daily.

Airlines and airports beefed up security measures after the outbreak of the Persian Gulf War, following Iraqi threats against Western targets.

Industry sources said the change was likely prompted by the Postal Service's fears that unscreened packages could carry explosive devices and that if such a device were to cause an air disaster, the service would be held liable.

Only a portion of the Postal Service's mail goes by commercial passenger planes. Jackman said the Postal Service pays commercial airlines about $10 billion a year to fly parcels and letters around the country. He said the airlines stand to lose as much as $1 billion from the security-related change.

For $100 million a year, Emery Worldwide, an air freight carrier company, currently operates for the Postal Service a fleet of 20 aircraft, the service's Eagle Network, which carries overnight and priority mail.

James Allen, an Emery spokesman, said yesterday the Postal Service "has expanded the contract for whatever they want to give us." He would not disclose the amount of the new contract or the amount of additional parcel mail the company will be asked to carry.

The Postal Service announced the changes at a meeting Tuesday with airline representatives and Federal Aviation Administration officials.