A 16-year-old Prince William County youth who collapsed at a party late last month died of cardiac arrest brought on by inhaling butane, apparently from a cigarette lighter, according to autopsy results made public by police yesterday.

Carlos Calo Garcia, a junior at Stonewall Jackson High School described as a model student by Principal Michael Campbell, died of what his peers have dubbed a "breath of fresh air," a county police officer said.

Butane -- a hydrocarbon compound categorized as an inhalant drug, along with aerosals, glue and freon -- has emerged recently as a substance with which youths are experimenting, according to Charles Sharp, a biochemist with the National Institute on Drug Abuse.

Sharp and health officials from Prince William, Fairfax, Prince George's and Montgomery counties indicated that butane is not thought to be one of the more popular substances in the youth culture, although they noted that it is difficult to get an accurate picture because butane is not illegal and is readily accessible.

A rescue official who attended Garcia the night he collapsed and died said that several youths at the scene indicated that butane was popular among teen-agers. The official asked not to be identified.

According to Sharp, butane is so new to the drug scene that there is not much research on it. Furthermore, he said he is not even sure why young people are starting to use it.

"I am perplexed as to what the feeling is," he said. "What do they feel? Do they expect themselves to get a good feeling or do they want to just get dizzy?"

What they should expect, the experts say, is possible death.

When inhaled, butane displaces oxygen in the lungs, causing suffocation. With larger doses, the heart stops because there is insufficient oxygen to circulate the blood, according to Toby Litovitz, director of Georgetown University Hospital's poison center.

In addition to depressing the central nervous system, which controls the heart and lungs and the body's other semiautomatic functions, inhalants can severely affect the liver and kidneys, said Keith Shuster, a director of programs on substance abuse in Prince William County.

Despite butane's long-term effects -- including addiction, weight loss, brain damage, muscle fatigue and impaired mental and physical abilities -- experts said they can be certain of its use only in cases of a severe reaction. "Unless there is a death, there is not a way it is going to come out," Sharp said.

On the night of Sept. 25, Garcia and three friends were heading for a party in northern Prince William County when they decided to stop at a drugstore and buy a butane lighter "to get a quick high," police spokesman Sam Walker said.

As they drove to the party, one of the youths opened the car door and Garcia slumped to the grassy shoulder of the road, Walker said. Other partygoers tried to revive him, and rescue workers were called.

Melinda Duncan, a captain with the Evergreen Volunteer Fire and Rescue Squad, said that when she and other rescue workers arrived, about 50 teen-agers, some of them screaming, were milling around.

Duncan said rescuers worked on Garcia for two minutes before one of the bystanders said Garcia had been inhaling butane. "I was yelling, 'Somebody tell me what this kid had! Teen-agers just don't fall unconscious,' " Duncan said.

While butane may be new to the list of inhalants, the concept of sniffing a substance to get high is not.

In a 1986 study of 15,000 high school seniors by the National Institute on Drug Abuse, 20 percent of those surveyed said they had tried inhalants. Nine percent said they had done so within the preceding year, and 3 percent said they had done so within the previous month.