Three American toads, all males, all sitting around in a Fairfax County swamp, listened to a tape recording Friday night.

The stars were out, the weather was balmy and the 30 people hunched around the toads' breeding pool were struggling to keep their mouths shut and their flashlights out.

The tape recorder, playing one of Cornell University's big herpetological hits entitled "Voices of the Night," belted out a number that turns American toads to thoughts of love. It was a pleasant, fast-paced, high-pitched beep.

The three toads responded, puffing up the air bags under their chins and beeping their beep of love.

Suddenly flashlights flicked on and jaws started flapping in the crowd of toad watchers. A mother pushed her three-foot-tall son toward the singing toads. "There it is," the mother whispered. The boy, seemingly unimpressed, said, "Hi, mommy."

Never before in its three-year history, has a "Frog Romp" been so successful. Never before in a frog romp have so many people seen so many frogs sing so many songs. That, at least, was the assessment of naturalist Dan James of the Fairfax County Park Authority.

James, 28, who wore a simulated frog on his shirt Friday night, three years ago thought up the idea of bringing people to Lake Accotink Park near Springfield to look at frogs.

On warm spring nights male frogs and toads sing to attract female frogs and toads to breeding ponds.

On such warm spring nights, however, male frogs and toads are not without problems. It is not all singing and sex. A male frog or toad frequently mistakes a male of his species for a female and also gets his species confused. "Toads and frogs," James explained, "aren't very smart."

A male frog or a toad has three basic relations to the world. If a creature is smaller than he is, he tries to eat it. If a creature is the same size, he tries to mate with it. If a creature is bigger, he flees from it.

An American toad, James said, "will clasp another male (for mating) but will quickly get off when he realizes what he has done." The affronted toad, James said, will utter a "get off me Jack" warning.

Friday's frog romp, which attracted 300 children, parents and other adults, was divided into two periods: frog familiarization and frog watching.

During the first period, James told the assembled 300 why he likes frogs. "Frogs don't hurt anyone. They just kind of hang out in the swamps, eat bugs and sing." James introduced, using slides and taped voices, the 10 species of frogs and toads that live in the Lake Accotink swamp.

The naturalist spoke affectionately of the spring peeper, a frog with a "big cross on its back, nice little suction cups on its toes" and a song like "sleigh bells." James also introduced the American toad, which he called "common and ugly" but possessed of "beautiful song."

In the crowd, soon after James played the song of the American toad, a toad responded. "We found this toad seven or five minutes before the show started," explained Chris Anderson, 8, of North Springfield. "We just walked out in the swamp and found him."

The toad was in a special toad box and it didn't sing when James introduced other swamp dwellers.

Crowd members had different reasons for giving up their Friday night to amphibians. "I'm into swamps," said Carole Miller, 31, a nurse at Georgetown University Hospital who came with her boyfriend and held hands.

Pati Young, 22, a legal secretary from Washington, said she is a "frog freak." She wore a T-shirt with three frogs on it; her license plates read TOADS. Her friend, Carol Newmeyer, came along because Pati could not find anybody else willing to walk in a swamp.

After 20 minutes, frog familiarization ended, and the 300 participants broke up into six groups. Dan James sat his group on the side of a grassy hill and told them to keep their hands off the frogs. Rubbing human fingers over a frog's clammy skin, he said, dries up the skin and kills them.

"So," asked 8-year-old Scott Signori, sensing the awful thruth, "we can't catch 'm, huh?" James said no.

James and his group headed off along a little stream with muddy banks. The frog rompers were equipped with flashlights and rubber boots. Most children were equipped with a parental hand to keep them out of mud.

It was, as James told the group, "a beautiful night for them (the frogs and toads) to croon their tune." Spring peepers and American toads aplenty performed for James and the group in the glare of flashlights. James said never before had they sung in the spotlight.

Kimberly Smoot, 3, who moved to Virginia last July, said she was not overly impressed by the Fairfax County singing frogs. She said she'd seen the same thing in Los Angeles.