Who's new at Oxon Hill Farm?

The National Park Service farm's newest resident, a calf born April Fools Day, doesn't have a name. Officially, that is.

"We considered calling him Dodo, because at first he didn't know how to nurse," said ranger Helen Smith, introducing a visitor to the farm's new crop of animals. "He kept trying to nurse on his mother's neck. We thought we'd have to bucket-feed him."

Smith, who wears overalls and looks like a real farmer but confesses she picked up most of her agricultural knowledge since she came to Oxon Hill Farm, said that means putting powdered milk in a bucket with a long nipple on it and sticking it in the calf's mouth. Dodo finally found the real thing.

"In big production plants, they take the calves off the mother right away, but we let the babies stay with their mothers because we only need enough milk for our hand- milking demonstrations,' Smith said. 'We don't usually pasteurize the milk, so we just give it to the pigs."

Dodo is romping around the fenced hillside she shares with nine other bovines of several varieties. While her mother, a Golden Guernsey, sits near the food trough, the calf chases after an elderly Jersey cow.

"That cow doesn't have any milk, or else she'd probably nurse the calf," Smith said. "We're a replica of a turn-of-the-century farm in most ways. But a real one wouldn't have kept a variety of breeds. We do it so people can see them. The animals usually give birth at night. You just come in in the morning, and there are the babies. We have three vets on call if we need them. One's been here every day this week for Sam."

Sam, the farm's veteran horse, is reclining under a tree, suffering from such trials of old age as colic and impacted bowels.

"He's our famous horse," Smith said. "He's very smart. If you ask him a question, he nods his head, and he'll kick his stall if he wants more food. He always did just what he wanted. Once he was pulling a wagon of VIPs, and he didn't want to work. So he pulled them under that tree there and one of the ladies was wearing a wig and it ended up on a branch."

Sam may be smart for a horse but, according to Smith, the most intelligent animals on the farm are the pigs.

"They're rated with elephants in intelligence. See those water spigots? They work just like water fountains and the pigs know how to use them to get a drink. The other animals here couldn't do that."

There are three little pigs cavorting in the mud, survivors of a litter of eight.

"She wasn't a good mother," says Smith of the sow, who is zonked out in the sty. "She just lay down on the other five and killed them. We won't breed her again. It seems if a sow isn't a good mother once, she never will be. Sows can have litters of up to 24, and the gestation period is only four months. We try not to breed them more than twice a year."

One of the piglets is spotted, and the other two look as if they might be pink under their mud coating.

"In any litter, we get a complete variety because all our pigs are mixed breeds," Smith said. "They roll in the mud because they have no sweat glands. Without cool mud they'd die in hot weather."

The three baby lambs in were not born on the farm but are orphans from Beltsville. Normally there are spring lambs born at Oxon Hill Farm, but this year nobody realized that the ram had been castrated.

"Lambs can be weaned very early," she said. The three orphans, now two months old, are eating grain out of the same trough as the adult sheep and the goats, which share their paddock. One baby goat is sleeping under the hay rack, and the other is kicking up its heels in the field.

The goats were born in February. "We didn't want them to be born in the dead of winter, but somebody donated this male goat . . ." she said, citing another example of how family planning on the farm is far from foolproof. SPRING ON THE FARM Oxon Hill Farm is free and open daily from 8:30 to 5. Take Beltway Exit 3A and follow signs to the farm. Milking demonstrations are at 10:30 and 3:30. Demonstrations of wool processing will be given May 9 and 16 from noon to 4. On May 15, visitors may ride to the lower fields in a hay wagon to watch corn planting from 1 to 4. May 23 is "Sheep to Shawl" day; the sheep will get their annual haircuts at noon and the shearing will be followed by demonstrations of spinning, weaving and dyeing. All events on the farm are weather permitting. Call 839- 1176 for last-minute information.