The U.S. Postal Service is investigating the origins of a box received yesterday by People for the Ethical Treatment of Animals that contained the bloody remains of a small animal and a note declaring, "Happy Holidays, PETA!"

The package, which was mailed to the group's headquarters in Rockville, contained a cat-sized animal whose legs had been severed and placed next to the skinned torso in a plastic bag. It has been traced to Louisville, Ohio, a suburb of Canton, according to Louisville Postmaster Alan Broemsen. A bogus return address, for the Stark County Humane Society, was written on the package, he said.

PETA officials said the package was the latest in a series of disturbing incidents targeted at the animal-rights group in recent months. Last week, employees received a dead hamster in the mail, and on another occasion, a bloody heart from an unidentifiable animal also was received in the mail by the group. In 1989, PETA worker Robin Walker returned to her Hyattsville home to find the carcass of a deer on her doorstep. Last year, a large mound of manure was dumped at the entrance to PETA headquarters.

Of the latest incident, PETA spokesman Daniel Mason said, "It's certainly a horrible thing, not from our standpoint, but to think that people have such little respect for life. It's understandable that they would target us, because we're a peaceful organization and they obviously prefer violence."

Mason said he is not aware of any recent PETA activity in the Canton area, but said, "We are known nationally."

A Postal Service spokesman said that it is not clear what the penalty would be in such a case. Said Postmaster Broemsen, "Of course, it is illegal to mail a dead animal that is not, shall we say, biologically prepared for experiments . . . . We will continue to investigate."