The colony of 70 carpenter ants flown aboard the space shuttle Challenger last June died of dehydration before they ever left the Earth, the high school students who built the ant colony experiment said today.

"It is our opinion after exhaustive tests that the ants died of rapid dehydration when their cannister was purged twice with dry air long before liftoff," Tasha Freeman, a student at Camden High School, said at a news conference. "We have concluded that the relative humidity of the air in the container after the second purge was one-tenth of 1 percent, drier than the driest desert on Earth."

Students at Camden and Woodrow Wilson high schools, who devised the experiment that was paid for by RCA Corp., said the ants probably died no more than 48 hours after they were placed aboard Challenger seven weeks before liftoff. It was in those first 48 hours that the experiment was purged with "commercial dry air" to cleanse the ant farm.

In a report they released today, the students said a microscopic examination of 100 sugar cubes placed inside the farm to feed the ants showed only 112 tiny bites in the cubes, suggesting that the ants had almost no time to eat.

"If the ants had been alive any longer than a few days those sugar cubes would have far more and far bigger bites in them," said Luis Sepulveda, a student at Woodrow Wilson High School. "And if they had lived at all on their trip in space, the sugar would have been just about consumed when they returned to Earth."

Camden High School's Freeman said the students worked with biologists at Temple University in Philadelphia and their own science teachers to devise ways of testing four theories of why the ants died.

One theory was that the ants suffocated in space when the sphagnum moss in which they lived absorbed oxygen and released carbon dioxide whenever the ants were in the dark because of photosynthesis.

A second theory was that the soil in the ant colony contained some kind of poison.

Analysis showed that the soil was clean and nontoxic.

Another theory was that bacteria or fungus could have been introduced by the students when they placed the moss, the soil and the wood that the moss grew on in the ant farm. An exhaustive test showed that the only bacteria present in the ant farm at the end of the flight through space was ordinary bacillus, which is not toxic to any living thing.

Nicholas Timpanelli, the science teacher at Camden High School who supervised the student experiment for the last five years, said he would like to see the experiment repeated with modifications.

Timpanelli said a device could be built into the ant farm that would introduce a spray of moisture after the farm was purged.

"It would be like having a humidifier inside the ant farm," Timpanelli said. "We think that's all it would take."

Timpanelli said he is proud of the almost 300 students at the two inner-city high schools who devised the experiment and analyzed why the ants died.

He said that they "put in a lot of extra work, although most of them had no idea of how to go about it when they began this project."

Since the ant autopsies suggest that the blame for the ants' death should fall on NASA, the space agency has indicated that it may allow the students to repeat the experiment. RCA has said it will put up another $10,000 to reserve space aboard some future shuttle flight so the students can get a second chance to discover how carpenter ants survive a week of weightlessness in Earth orbit.