Post Office Braces as Strike at United Parcel Is Feared : Mail: Officials say the system cannot assume the whole UPS load. A contingency plan would limit packages shipped.

The U.S. Postal Service, bracing for a potential strike at United Parcel Service, Tuesday announced contingency plans that officials hope will avoid disruption of first class mail if a truckers’ union walks out after expiration of its contracts next week.

The plan assumes disruption for large shippers and is designed to limit the number of parcels individual mailers can drop off each time they visit a post office. In addition, the Postal Service said that it will deliver some packages only if they are first somehow shipped to a post office within the recipient’s city.

Moreover, the service said, there could be delays in its second-day mail delivery service, perhaps by a day or more.

The Postal Service announcement followed the release of a letter from UPS officials to more than 1 million of its regular customers, warning them of possible service disruptions after July 31 should the International Brotherhood of Teamsters reject the UPS contract offer.

Voting on the contract is under way and a count is expected next week, said a Teamster official, who added that the union leadership opposes the contract offer.

UPS said that packages scheduled for delivery after July 31 “could, in the event of a work stoppage, be subject to a considerable delay.”

Michael Coughlin, deputy postmaster general, said that the Postal Service is worried that its regular mail service could become paralyzed if a Teamsters’ strike dumps UPS’ daily packages on the nation’s post offices. Even with the advance plans, “there’s no way the Post Office can absorb UPS’ operations,” he said.

UPS currently handles 10 million packages daily--20 times more than the 500,000 packages delivered daily by the Postal Service. UPS also delivers 300,000 overnight packages, a third more than the government service.

The Postal Service, however, continues to hold a 3-1 lead in two-day delivery parcels.

Under the Post Office’s contingency plan, shippers with five or more packages would have to call a toll-free, 800 number to find the post office within the ZIP code area where the deliveries are to be made. For example, if a mail-order company wanted to send a dozen packages from its warehouse in Maine to customers in Southern California, the company is likely to be told that it must arrange to leave the packages at a designated post office within the Los Angeles area.

“The responsibility of getting the parcel to the (designated post office) location is the shipper’s responsibility,” Coughlin said, adding that postal officials will meet today with trucking companies and other freight forwarding firms to coordinate their plan with their operations.

Postal officials, who are monitoring the volume of packages coming from large shippers, said that they would decide by Friday whether to institute the plan.

Parcels in groups of four or less would continue to be accepted, as usual, at any post office. Similarly, there would be no restriction placed on paid overnight or first-class mail delivery.

“These rules will not affect the American consumer or small businesses which mail two or three packages a day,” said Azeezaly S. Jaffer, a Postal Service spokesman. “The real focus is on the big shipper.”

Teamsters struck UPS operations in 15 states in 1977, a company official said, noting that the shipping firm’s national operations have never been curtailed by labor problems.