Animal rights activists cut through a chain-link fence, smashed several padlocks and took 27 cats from an Agriculture Department research facility in Beltsville -- including 11 cats infected with a parasitic disease that is particularly dangerous if contracted by pregnant women, USDA officials said yesterday.

The disease, transmissible through feline fecal matter, can cause fetuses to contract an infection and later suffer blindness, mental retardation and hydrocephalus (brain inflammation), said Hubert Kelley, spokesman for the USDA's Agricultural Research Center in Beltsville.

A group calling itself the Band of Mercy took responsibility for the incident, asserting that the cats, along with seven African miniature pigs, were "liberated" from government researchers who practiced "animal abuse with no clinical significance."

The intruders at the center, off Rte. 1 in northern Prince George's County, spray-painted slogans on exterior laboratory walls, including "Stop the Slaughter" and "Animal Liberation," and they left behind poetry and vegetarian recipes.

The People for the Ethical Treatment of Animals, acting as representatives for the Band of Mercy, issued a statement saying that the cats "were not scheduled to be treated. Experimenters simply record their dehydration, diarrhea, high fever, weakness, inflammation of the heart and liver and pneumonia before killing them.

"The cats are all currently under veterinary care and will later be placed in caring, permanent homes."

"I hope there aren't any pregnant women in those caring homes," USDA spokesman John McClung said in response. McClung said that the FBI, the USDA's office of the inspector general and the U.S. Park Police have been called in to investigate the theft and retrieve the animals. By late yesterday, however, no arrest had been made. The theft occurred between 3:30 p.m. Saturday and 9:30 a.m. Sunday.

Charges in the case could include trespassing and theft of and damage to government property.

The cats infected with the parasite were removed from the laboratory of Dr. J.P. Dubey, a USDA veterinarian specializing in research on the common parasitic disease toxoplasmosis. Dubey said that the disease cannot be transmitted by touching cats but only through contact with cats' feces or by eating undercooked meat of animals that have been exposed to the parasite by grazing on feline fecal matter.

"In the United States, toxoplasmosis is a very common infection," Dubey said. "About 40 percent of the people have been exposed to this parasite." Normally, it will not cause disease, except in persons with lowered resistance, Dubey said.

Approximately 3,000 children a year are born infected and can have serious illnesses, Dubey said. The parasitic disease causes abortions in farm animals such as sheep, goats and pigs.

The cats, intentionally infected with the parasite for experimental purposes, were part of Dubey's study of the transmissibility of the disease. "One of the unanswered questions," he said, "is if a cat will transmit the parasite once a life or several times; if you have a cat whose resistance has gone down, whether it will re-shed the parasite in its fecal matter.

"Nobody knows what percentage of people become infected by eating meat or what percentage get it by coming in contact with cats' feces," Dubey said. "If we knew that, it would be a major discovery.

"I have three years of my research down the drain," Dubey said. "Hundreds of hours and thousands of dollars are wasted."

Dubey said that there is no drug known to cure cats infected with toxoplasmosis. The only treatment, Dubey said, "is when the cats are suffering. You can slow down the division of the parasite, but it can never be completely killed."

Dubey disputed the assertions that the animals were abused: "I am a veterinarian. I could not in my dreams mistreat animals."

The Band of Mercy's last major "animal liberation" occurred in April 1982, when 42 rabbits were seized from the University of Maryland at College Park.