IN THE WATER floats a naked young man, eyes rolled up in panic, arms flailing, his left leg crunched off at the knee and trailing blood. Lunging just inches from his head is what looks like the designer model for Jaws IV -- a gleaming-toothed monster shark, malice rippling through its frenzied body.

The guy in the water is a goner, for sure.

But wait -- next to him, heart-rendingly out of reach -- is a boat manned by sailors intent on rescuing our hero. Two stretch out their arms; one flings a rope; another aims grimly with a harpoon at the shark below.

Will the rescue come in time? And even if the harpoonist slays this shark, what about that menacing fin behind him? Could the oarsmen steer close enough for rescue before the victim loses his head?

Welcome to the wonderful world of art.

"Kids love this painting -- you can't get them away from it," says Lynn Russell at the National Gallery of Art, which offers, this and every Saturday in May, an art-appreciation tour for families with children aged six to twelve. "I always start by asking them what's going to happen, and usually we figure that there's no way he'll be rescued; the shark is just too close."

In fact, she says, spilling the beans, the man in the water -- Brook Watson -- was saved: He commissioned the painting by John Singleton Copley in the late 18th century.

The painting serves as a good tool for teaching things like balance (why is the shark in the middle of the painting?), line (why is everyone placed in a zig-zag pattern?) and color (what feeling do these cold colors convey?). And it serves Russell's larger goal -- helping folks learn how to really use their eyes.

"People don't know how to notice things," she says, "which is one of the reasons we have all this ugly architecture around. Most people grow up visually crippled."

She's out to change all that by training children (and their parents) how to "really look at a painting. This doesn't depend on something they've studied in the classroom or how smart they are; it's all right in front of them."

Kids are good at this sort of observing, she says, "though they haven't been trained on how to express their visual knowledge. I'll ask them a question and they'll tell me, 'It's that guy over there in the picture,' and I'll have to keep pulling at them until they say, 'It's the guy in the red bathing suit next to the beach towel.' "

In front of George Bellows' boxing painting, "Both Members of This Club," she'll ask who's going to win the fight depicted, and why. "The why tells you how the child is thinking and what he's noticing," she says.

She likes to draw children to the little clues in a painting that contribute to its feeling. One of Bellows' boxers -- the clear loser -- has a red face, "and some kid will always say, 'He got his face smashed in,' " she says. "Then I'll ask them what the color red reminds them of, and eventually somebody will say blood and pain. Then they'll see that Bellows was trying to show the pain of that moment."

She encourages the kids to play with line, like the curves that wave through Mary Cassatt's "The Boating Party." "I ask them what curving lines like this," she says, her arms flowing languidly through the air, "make them feel like, and they usually decide it's relaxing, like you feel at the beach."

Around sculpture, she tries to get the audience to think like sculptors, asking them, "What's the first thing you have to do when you've got this block of marble?" They'll settle on a subject -- a child, perhaps -- and then she'll ask, "What should you have in front before you start? First they'll say, 'A photograph of a boy,' and we'll have to discuss what they did in the days before photographs.

"Then you'll get this, 'ooo, ooo,' with kids waving their arms in the air, and one will say, 'A child!' "

This kind of reasoning is easy to learn and adds a depth to the viewing of any work of art, Russell believes. "People really are perceptive, if you guide them a little," she says. "And we hope they'll see that with a little practice they can learn to do it by themselves."

It's a particularly good skill for families to learn together, Russell says, because it can make a real difference in the kinds of experiences they have in museums. "A lot of families don't do things together, which makes vacations kind of a strain. They need a little help in learning to take children to a museum."

If the response to this month's tours is good, the Gallery hopes to offer more family- centered programs later in the year. The free Saturday morning programs, available to the "first 80 or so" people to make reservations, begin with a film and follow with a tour.

"We're starting with Sal Bruno's 'Art Elements: An Introduction,' which shows a lot about line and shape and color," Russell says, "and we'll work off of what they learned in the film on a tour of the West Building."

Subsequent Saturdays will focus on the East Building, American Art, and Gods and Heroes. "We couldn't find a film on classical mythology," Russell says, "so instead we're showing one on African folktales and myths that week, which I think is even better; it shows the universal elements that appear in all mythology."

FAMILY TOURS AT THE NATIONAL GALLERY OF ART -- Each program runs from 10 to 11:30 every Saturday through May. Groups will have individual instructors and average no more than about 20 persons. Reservations are required. Phone 842-6249.