The three 30-pound cubs scampered around the grass yesterday at the National Zoo, chasing each other, rolling over and nipping at their mother. They behaved just like house cats, but they were actually practicing to be grown-up, meat-eating tigers. For Mike, Eric and Chrissie, born in June at the zoo, it was their public debut. They had been released from their indoor den to the outside world for an hour or so each day for the past week, but not when zoo visitors were watching.

As the press and fascinated children looked on, one cub even ran over and pounced on its mother. She swatted it softly, then gently put its head in her mouth--a quick lesson in how to be a predator.

"Look at that!" said John Seidensticker, the zoo's curator of mammals. "It's wonderful!"

The three-month-old cubs are smaller versions of their mother, with a dark orange coat and narrow black stripes. They have white tufts of fur behind their ears. They drink their mother's milk and eat horse meat, just as she does.

The cats created a sensation among zoo visitors who wandered by in the drizzle. Children pointed at them and shouted, "Baby tigers!"

"Oh, they're fighting!" a little boy shouted, as the small tigers pawed each other.

"No, they're playing," Seidensticker told him.

One sweating runner stopped abruptly as he headed past their grassy perch, and stared, panting.

"It's worth losing a little of my time," he said, glancing at his watch before moving on.

Zoo officials say the cubs will be let outside at 11 a.m. each day, probably for about two hours. How long depends on their mother, Kerinci, a 14- or 15-year-old (zoo officials aren't sure), named for a volcano in Indonesia.

The National Zoo has put up Web cams at the tigers' indoor enclosures, which can be reached via the zoo home page: www.si.edu/natzoo.

The three cubs were born June 24. Eric and Chrissie were named after children who won a poster contest about tiger conservation; Mike was named for zoo director Michael Robinson and for I. Michael Heyman, outgoing secretary of the Smithsonian Institution. They are Kerinci's third litter at the National Zoo.

"She's a great mom," said one of her keepers, Jeanne Minor. "She's got it down."

With another male, Riau, Kerinci produced two cubs in 1992 and two more in 1993. All but one--a daughter, Soy--are at other zoos.

The cubs' father is Rokan, a male named after a river in Sumatra. Zoo officials said he knows the cubs are his and licks them through the mesh fence that separates his indoor enclosure from theirs. But keepers intend to breed him with Soy, so they don't want him focused on his children, rather than on being a stud, right now.

There are fewer than 500 Sumatran tigers living today, including about five dozen in North American zoos. They are native to the Indonesian island. The zoo cubs' conception--the natural way--was permitted under an international breeding program intended to preserve an animal population with wide genetic variation.

Seidensticker said that despite the small Sumatran tiger population, there are no immediate plans to try to increase their numbers in the wild. The cubs, he said, are an "insurance policy" in case wild populations drop sharply.

Because of the international breeding program, Kerinci's three cubs will be sent to other zoos. Seidensticker said he hopes they can stay for 18 months, about the same time they would stay with their mother in the wild.

After two hours chasing after her cubs outdoors, Kerinci was ready to go inside to eat and nap. She loped over to the gray door, followed by one cub. Keeper Wayne Millner let them in.

The other two cubs lingered outdoors. Millner walked outside (the cubs are not yet big enough to hurt him) and clapped his hands. But no cat likes to be herded. They hid in the tall bamboo, hissing.

He batted at them gently with a thin stick. One scampered off and was let inside. Millner returned to fetch the other. Finally it trotted to the door and went indoors to its mother.

CAPTION: Sumatran tiger cubs, born in June at the National Zoo, get a glimpse of the public. Officials said the cubs will be allowed outside at 11 a.m. daily for about two hours.

CAPTION: There are fewer than 500 Sumatran tigers, including about five dozen in North American zoos. These cubs eventually will be sent to other zoos.