Will the National Aquarium sink or swim?

The National Aquarium, home of the lemon shark, the red-bellied piranha, and the lionfish, is about to go glub unless a sudden public outcry is effective. The National Aquarium is the oldest aquarium in the country, begun during the Grant administration, over 100 years ago. And its budget of $286,000 is just fish food compared with the Moby Dick $695 billion national budget. But the Aquarium should go down the drain among the first budget cuts, says the Interior Department which has control over it, cutting deeply to please the Office of Management and Budget.

The US Fish and Wildlife Service, which presides over the aquarium for Interior, told Rep. Sidney R. Yates (D) of Illinois, chairman of the subcommittee on Interior, at hearings this month that it should pull the plug on the Aquarium. But there had been an unexpected outpouring of 'save the Aquarium' letters, calls, even poems, from concerned adults as well as lots of schoolchildren who sent in their share of Crayola whales.

That public protest is part of the record of the Yates subcommittee, which is scheduled to decide soon on the fate of the Aquarium.A spokesman for Representative Yates says Yates doesn't want to indicate his decision now, that he is studying the issue and keeping his options open. A decision will be made, the spokesman says, on June 9. One of the probable options, in view of the public clamor, is that the Aquarium will be kept open, but the public will be charged for the first time a minimal admission fee, considerably less than $1, to pay for its maintenance costs and needed renovations.

To understand what the outcry is about, you have to see the filtered, subterranean charm of the Aquarium for yourself. Some people expect it to be a gilled version of the National Zoo. It is not. It is an unpretentious aquarium , housed for reasons understood only by the subaqueous governmental bureaucracy, in the basement of the Commerce Building. (The old Bureau of Fisheries was in the Commerce Building.) You have to sign in to see the Aquarium, as though you were visiting the Central Intelligence Agency. You go down a murky flight of stairs into the dimly lighted exhibit hall, where 1,000 specimens, from Japanese carp to Indo-Pacific stonefish, swim in perpetual cycles.

There is a faint smell of brine, of seafood ded to the larger fish, a sort of moist excitement in the air, and the splash of a Japanese pool. Low tanks line the walls at eye level for children or short adults. So you can go eyeball to eyeball with the arawana from the Amazon Basin of South America. The arawana is nearly two feet of pale, silvery white fish whose beautiful scales, twice the size of fingerprints, turn an iridescent coral as it shimmers through the water. It has light blue shadows over its hooded eyes and a cynical mouth, turned down like the flap on an envelope. There are barbels (shaped like barbs) on its mean-looking jaw to make surface feeding easier.

In the tank next to it floats an ocellated featherback, a lavender-brown fish that looks as though portholes have been painted on its side. It comes from Burma and has a back that rises like a harp in the air. In the same tank with it, two grayish-green turtles are performing the rite of spring. He nuzzles her turtle neck, she boffs him away with a flipper, he pursues her with a lumbering stroke that verges on speedy, urged on by a small, cheering crowd of spectators.

Five kids towing two adults come barreling through the exhibit. "Where are the piranhas?" they want to know.

"Those teeny little things?" they ask increduously. The red-bellied piranhas glare out at them. They are six to eight inches long, an iridescent mauve and silver gray under the lights, their sides sprinkled with silver light like sequins. They are pudgy little fish with tiny, interlocking, razor-sharp teeth. The kids read the sign: "Piranhas are not the vicious, blood-thirsty creatures they are so often reported to be. . . ." But they don't believe it. They want to be scared. "Attack! Attack!" one of the boys says. "You know they can bite through that glass," a pigtailed blond girl says in a dulcet voice. When a whole school class comes through a few minutes later they race for the piranha tank.

But furst: "Look at the baby shark!" one of them yells. And they do. This is a lemon shark, actually a yellowish gray in color, this one only half the eight-foot size it will eventually grow to, and it swims restlessly in circles. Its roommate is a nurse shark, a pinkish gray color, which drifts lazily among the coral hunks at the bottom of the tank. It is called a nurse shark, we are told, perhaps because the female normally retains her eggs until they hatch.

There is fascination in every tank: the batfish, cream color with black stripes and a huge dome that makes it look like the star of the movie "Eraserhead." Or the poisonous lionfish, with its mane of fluttery gills that look like striped chiffon panels afloat in the water. With its iridescent cream and dark orange stripes it's lovely to look at, lethal to know: Its dorsal spines carry a powerful venom. Farther on there's a tankful of sea anemones, floating like long-petaled white crysanthemums in the water. They are actually waiting for dinner to swim by. When the unwary banded coral shrimp wanders by, the long white tendrils of the anemones turn lavender at the tips; as the prey is embraced by what are actually tentacles full of stinging cells, and dinner is digested, the sea anemone turns a vibrant shade of violet.

There's a drama in every tank at the Aquarium; small wonder that its fans, both children and adults, press their noses to the glass and never want to see it shut down.

The Interior Department does not agree. "It's a 50-year-old facility that needs extensive renovations," says Alan Levitt, chief of the Office of Current Information at the Fish and Wildlife Service. "The physical plant looks a lot like a dungeon; it's crowded, noisy, the tanks are not large," Mr. Levitt says. He points out that the Aquarium has a much lower priority at Fish and Wildlife than some of their other, more statutory responsibilities, like protecting endangered species and maintaining hatcheries. But he admits, "It's a popular tourist attraction here in Washington. It is so popular that it gets the lion's share of phone calls from the press --we've gotten five dozen calls on this subject, but not more than a dozen on the rest of the budget cuts."

Paradoxically, the person most knowledgeable about the Aquarium, its director , Craig Phillips, was not permitted by the administration that wants the budget cuts to testify at the Yates hearing. Mr. Levitt says Mr. Phillips as director of the Aquarium is only "the equivalent of a project leader, and we have 1,000 of those. He knows the Aquarium but he doesn't know about the priorities of the agency. They were asking questions about agency budgets and priorities." So the bureau's acting director, Dr. Eugene Hester, testified.

Mr. Phillips acknowledges that the Aquarium is "small potatoes" in terms of the big federal budget. But he points out that there has been an outpouring of "calls and letters from people all over the country who hope it will be saved because it belongs to the people. We've been very grateful for the tremendous amount of support." Mr. Phillips says he favors charging a small admission fee so that the Aquarium might become self-supporting and the needed renovations could be done.

Does he expect the Aquarium to sink or swim?

"We may be the last to know," he says.