Animal lovers here and across the country are mobilizing in an urgent effort to help thousands of pets and farm animals still stranded or left homeless by Hurricane Katrina and the floods that followed.

Wayne Pacelle, president and chief executive of the Humane Society of the United States, appealed yesterday for immediate federal, state and local assistance in the Gulf Coast area to save animals he said will die in the next few days if they aren't found, fed and sheltered.

"Animals are trapped by the thousands in their homes, and the clock is ticking," he said. "We need the government to help us, not with money but with rescuers. We need the Coast Guard, firemen and the National Guard. . . . We'll take care of the animals after they are pulled out."

Pacelle, noting that about 60 percent of households have pets, estimated that more than 50,000 animals might be in peril. His organization has received more than 2,000 calls from people who fled Katrina. Other organizations, including the American Society for the Prevention of Cruelty to Animals, also have been getting pleas for help. Many people left behind pets, especially cats, because they thought they would be gone only a couple of days.

Hundreds of animal welfare workers and volunteers, including some from the Washington region, are in Louisiana and Mississippi with mobile veterinary units, vans, boats, pet food and supplies, as well as holding pens for farm animals. The most crucial mission is the door-to-door rescue of the stranded pets, but officials said there also is a pressing need to ease the strain on crowded animal shelters and get pet food to those who have taken in stray animals until they can be reunited with their owners.

Locally, a team from the Washington Animal Rescue League returned from Louisiana early yesterday with a van full of 22 dogs. The animals, many of which were given up by their owners before and during the storm, are among hundreds that are being moved out of the Gulf Coast area to make room for other pets lost or left behind.

"If anyone is considering adopting an animal, please make a decision to do it now," urged Jennifer Brickman, the league's director of marketing. She said the van and league staff have returned to Louisiana to help with more animal rescues and veterinary services.

Several animal welfare groups are using their Web sites to help reunite owners with their pets -- and to solicit contributions to assist with their rescue efforts.

Many people who were trapped in their homes by Katrina said they chose to stay rather than leave without beloved pets. Animal rescue workers said yesterday that they are trying to find more shelters that will allow the people and pets to remain together.

"Some of these people will live on the streets and won't go to a shelter if they have to be separated from their pets," said Laura Bevan, the Humane Society's southeast regional director. "I respect that, because I wouldn't either."

In the District, Gregg A. Pane, the city's health director, said the makeshift shelter at the D.C. Armory "handled all comers, and that includes pets." Among the evacuees who arrived there Tuesday, he said, were three dogs, named Lucy, Ethel and Arthur; a kitten named Calli; and a parakeet named Peaches.

"We bent the rules a little, and the small, well-behaved animals were allowed to stay with their owners," Pane said. The evacuees "have been through a lot. . . . Many of them don't have ID or anything, but they managed to rescue their animals."

The animals brought to the armory are kept in cages and examined by veterinarians. Arthur, a large dog, had an eye infection and was too excitable to stay with his owner, Pane said. He is at the city's animal shelter, where his owner can visit.

In Louisiana, pet-friendly shelters are in short supply, said Joelle Rupert, who runs Animal Aid for Vermilion Area, a refuge in Abbeville, about 150 miles west of New Orleans.

"If there would have been something that was people/pet friendly, a lot of people would have left" before Katrina struck, she said. "They didn't want to get separated from pets. They are like members of the family."

Rupert said that pet owners have been turned away from motels and that a small Baptist church is the only place in Vermilion Parish offering shelter to families with pets. She said she is providing pet supplies to those who have managed to find housing.

In Natchitoches, a town about 275 miles northwest of New Orleans, the animal shelter was filled yesterday, making it harder to find room for newly found strays.

"I know one of the vets just took in five parakeets," said Tammy Hamm, the shelter's supervisor. "The owner . . . doesn't know how long she's going to be out of a home."

Two 8-month-old Shih Tzus arrived yesterday, brought in by a woman who said her husband refused a boat ride out of his New Orleans home because he couldn't bring his dogs with him. The shelter has taken in 15 pets, mostly dogs that are very attached to their owners.

"All of them have been in good condition," Hamm said. "But they are upset, withdrawn, and they are not eating. They are as traumatized as the people are."

Veterinarian Jocelyn Crawford of the Washington Animal Rescue League examines hurricane evacuee Sky at the league's offices in the District.