The tropical fish looked as happy as clams, swimming around in their tanks in the muggy heat at the 110th National Aquarium birthday celebration yesterday. But the lobsters, which were brought in for guest star appearances (with their claws bound), were in the touchy/feely tank and began to look more and more like lobster thermidor.

Eve Fuerth, 15, a volunteer in charge of making sure the starfish didn't eat the clams and that no small child fell into the "discovery" tank, was afraid the lobsters were dying. "This water is just too hot for them. They like cold water," she said, with great concern. The malfunctioning air conditioning had turned the basement air into a tropical island climate, and some of the non-finned guests began to feel as though they also were done enough to be doused with hollandaise sauce.

But then everybody cheered up when Midge Baldrige, chairman of the National Aquarium Society, thanked all the volunteers. Effi Barry, the mayor's wife, handed out prizes for the fanciest fantasy fish and cut a blue cake shaped like a fish. Guests poured down gallons of pink punch. Everybody agreed the exhibit on fish environments was wonderful, and thatthe new movie theater, which will show films on sea life, looked promising.

After guests had gone, aquarium manager Brian Montague fished out the lobsters and put them in a nice, icy-cold tank--just in time, he said.

Baldrige said she organized the society in February 1982 after the U.S. government stopped funding the aquarium. "I heard about the need," she said, "because my husband works upstairs." (Malcolm Baldrige is secretary of commerce.) The aquarium has been housed for more than 50 years in the basement of the Commerce Department.

"It seemed as though we could, with a small amount of effort, do something which would benefit not just the tourists, but the children of our area," Midge Baldrige said.

"With some other charities, you can't see you've made a difference," said Nina Selin, society vice chairman. "But with this one, we've kept it open."

The society's counsel, Thomas Lamia, said the group was granted a license from the General Services Administration.

"The society in turn has a contract with Guest Services Inc., who operate the Commerce cafeteria, to staff and maintain the aquarium," he said. "GSI collects the $1 fee and the proceeds of the gift shop, but pays all the day-to-day costs, including replacing any fish that expire. They also donate $10,000 a year for each of the three years on its contract."

"We are trying to get lots of people to pay $100 to adopt a fish," said Selin. "We raised more than $80,000 at our first fundraiser and we're having another in September. Fish cakes and fishing clothes. We should do well."

Since the society took over, the aquarium has acquired 300 fish, 50 of them new species, and eight new fish tanks, including the hands-on tank where children can fish with their hands for the less snappish sea life. "We've gotten rid of people and put in fish," said Selin. "The new tanks replace offices."

In all, there are 58 tanks, holding 1,000 marine creatures, half freshwater species and half saltwater. Thirty percent of the 180 different species represented are American.

Baldrige paid tribute to the volunteers from Michael Graham's American University design class. Another class came up with the "Come Sea Us Now" slogan. Local schoolchildren Erik Kunze, 12, Nabil Khadduri, 10, Heather Freese, 12, and Mark Goldberg, 5 1/2, won prizes for their drawings.