Mother and daughter koalas, snatched from their cages at the San Francisco Zoo by two teenagers who apparently wanted to impress their girlfriends with exotic Christmas presents, were recovered, safe but scared, this morning.

"We are ecstatic. They appear to be in excellent health," said a visibly relieved David Robinett, the zoo's general curator.

One suspect, a 17-year-old, is under arrest at the Youth Guidance Center on charges of burglary and grand theft, and police believe they know the identity of the second suspect, who is 15.

The koalas, Pat, 15, and Leanne, 7, were stolen from their zoo home sometime after 6 p.m. Tuesday and were recovered before dawn today in the Visitacion Valley home of the arrested youth.

Police, responding to a midnight anonymous tip from someone apparently fearful for the safety of the cute but acutely sensitive marsupials, surrounded the Sparta Street home around 2:30 a.m. and spotted them through a window.

San Francisco Police Inspector Lewis Bronfeld said the thieves "stole them (the koalas) for their girlfriends for Christmas gifts. . . . They were trying to feed them leaves, oranges and carrots, unsuccessfully. . . . They were real live Christmas gifts."

The suspects initially placed the koalas in a plastic bin in a bedroom but the panic-stricken pair was found in a hallway, and the house was littered with their droppings.

Bronfeld said while "a number of people were out there (at the zoo), scoping the place out on Christmas, we're pretty sure who went in there." Police found gloves, which zoo attendants use when handling koalas, in the Sparta Street home, whose principal occupants are not suspects in the burglary.

San Francisco Zoo veterinarian Dr. Freeland Dunker said that the two koalas showed "no obvious evidence of trauma or mistreatment," but that the reclusive animals were obviously "stressed because of the displacement."

The koalas had evidently eaten no food since being removed from the zoo -- the thieves evidently being unaware of their finicky appetites.

"They were starving when they got here," zoo spokeswoman Nancy Chan said. "They were eating so much and so fast, it was quite a sight."

Nancy Rumsey, the zoo's koala keeper for the past 10 years, who first noticed that her charges were missing, said Pat was even eating out of her hand -- highly unusual behavior for a creature that is ordinarily secretive in its eating habits.

Koalas have no body fat and, when they're off their feed, can lose 10 percent of their body weight overnight. Zoo officials were afraid that Pat and Leanne would die if kept away from their home for more than a day.

Pat, who at age 15 is a geriatric koala with badly worn teeth, is especially frail, Chan said.

Police believe that the thieves smashed through a skylight of the exhibit building and entered through a furnace room door to get at the koalas, taking the first two they encountered. "And they terrorized the others," Chan said.

Bronfeld said the animal-nappers had probably used a cardboard box made to carry heater filters to haul the koalas out, then left the box outside the building as they fled.

"The general public may see an animal and think it's cute and cuddly, (but) without proper care these animals can be in serious trouble very quickly," said David Robinett, general curator of the zoo.

That care includes a specialized diet of selected eucalyptus, a 65 degree environment and minimal stress. Without those things, the animals suffer dramatically and may die of dehydration within days.

Police early on focused the investigation on two men: one seen in the koala keeper's area of the exhibit about 4 p.m. on Christmas Day, and another spotted minutes later in the same area.

Koala keeper Rumsey told investigators that the first man claimed to have followed a peacock into the area, but then began asking about koalas. While he was in the keeper's area, the man asked her several questions that, Rumsey said, "kind of made the fur on the back of my neck raised."

"He just asked me how do I get a koala, and where do you get one and can you buy one?" Rumsey said. "He kept asking me more questions, and he left after a few minutes of that."

About 15 minutes later, she heard a noise on the roof, then a second noise followed by a loud sound that turned out to be a koala jumping from perch to perch. She looked up and saw a man's hands on the skylight. Security guards were summoned, but they found nobody.

A few minutes later, Rumsey and another zoo official saw the second suspicious boy looking into the koala viewing window, and asked him whether he had seen anything strange happening. He responded, "I didn't see anything, I just got here," Rumsey told police.

Zookeepers discovered the koalas -- native to Australia, where they are considered a threatened species -- were missing when they checked the habitat about 9 a.m. yesterday.

The theft of zoo animals is rare but not unknown.

Last June, a female river otter named Harriet was stolen from her watery pen at the Oakland Zoo. She left behind her mate and a 10-month-old baby, and she has never been found.

In September, a 3-foot-long San Francisco garter snake, an endangered species, was stolen from the San Francisco Zoo. The pencil-slim snake, named Sarah was one of just 13 San Francisco garter snakes in American zoos.

And in 1997, a broad-nosed caiman, a 4-foot-long, 9-year-old crocodilian, was stolen from a heated pool in the San Francisco Zoo's aviary and was missing for more than two months before being found in San Jose, tied to a post. It was badly dehydrated but alive.

Koalas, native to Australia, normally consume a pound or two of new shoots from among the 10 pounds to 20 pounds of eucalyptus leaves of various varieties offered up as "browse" each day -- and they are finicky eaters.

The mother and daughter koalas -- each weighs about 11 pounds -- are part of the zoo's collection of seven koalas. The animals are not bears as many people believe; they are marsupials, or pouched mammals.

Pat came to the zoo in 1986 from Australia and subsequently had two offspring, Leanne and Janie. Leanne has had three male offspring over the past few years: Gilbert, Cox and, last year, Brandt.

The San Francisco Zoo is among only about a dozen institutions in the nation with a koala collection, given the financial and logistical challenge of maintaining the koalas.

San Diego Zoo has the largest collection of koalas in the United States, more than 30, said zoo spokeswoman Christina Simmons. None has been stolen. Simmons declined to say whether her zoo's koala exhibit is equipped with an alarm system.