A Seattle-based group calling itself the Northwest Animal Rights Network is urging the public to boycott Federal Express Corp. until the cargo airline stops carrying live horses destined for slaughter from Seattle to Japan.

In a letter distributed to customers outside Federal Express' main Seattle office, the group said the horses endure a long, frightening and stressful journey from Seattle-Tacoma International Airport and upon their arrival are slaughtered for food. Horsemeat is considered a delicacy in Japan and other Asian cultures.In a statement, Federal Express said live animals are shipped under strict government guidelines and veterinary supervision, and that handlers are on board during the flight.

The company also said it can't be responsible for determining the diverse wants and needs of the many countries it serves.

"We would be assuming an untenable role if we sought to set ourselves up as an arbiter of these cultural differences," it said.

Those explanations don't appease Dr. Wayne Johnson, one of the group's directors.

Federal Express "assures it's being done the humane way . . . We say there is no humane way," he said.

Dr. Johnson said his group has spotted live horses, as many as 150 to 200 at a time, being carried in double-decker trucks from a farm in Yelm, Wash., an hour southeast of Seattle, to the airport. Soon after, the horses are placed aboard Federal Express freighters for the trip to Japan.

Although the group said it takes issue with the entire shipping process, it has aimed principally at Federal Express because of its high-profile nature. ''The question becomes where do you focus the pressure," Dr. Johnson said.

Shirlee Finley, a Federal Express spokeswoman, said it's the first time to her knowledge that the company's transport policies have been challenged on an ethical level. She estimates that the shipments occur twice a month.

The U.S. government permits the shipping of live horses to Japan for slaughter as long as the animals receive a U.S.-origin health certificate from the Agriculture Department and the shipments meet the requirements of the receiving country.

"That's all we require for export," said Dr. Lisa Ferguson, a USDA official based in Hyattsville, Md., a Washington suburb.

Some competitors of Federal Express are unwilling to follow its lead. United Parcel Service refuses to ship any living thing except for items such as shellfish. Nippon Cargo Airlines ships live horses to Japan but only for racing or breeding purposes. It will also ship already-processed horsemeat.

Peter M. Diefenbach, marketing manager for Nippon Cargo in the United States, said live horses are one of the most expensive commodities it carries. It charges the full tariff rate as well as an additional surcharge that compensates the airline in part for the large amount of space the horse occupies.