In what may have been the first American rocket launch in a snowstorm, the United States yesterday put into orbit the first satellite to study the ozone layer of the stratosphere that protects the earth from the sun's searing ultraviolet light.

After three postponements because of bad weather, a 324-pound spacecraft called the Applications Explorer Mission left on top of a Scout rocket from Wallops Island, Va., at 11:16 a.m. in 16-degree temperatures and falling snow.

It was the 99th launch of a Scout, the first time in temperatures below freezing, and as far as anyone could remember, the first time any U.S. space launch took place in a snowstorm.

On board the Explorer satellite is a $3-million instrument that will measure the ozone and dust layers in the stratosphere, which many scientists believe hold the clue to the future of the Earth's climate.

Recently, there has been worldwide concern over fluorocarbon gases that serve as propellants in many aerosol spary-can products. The fear is the fluorocarbons rise high in the stratosphere and are broken down by the sun's ultraviolet rays, releasing free chlorine that destroys the ozone.

Scientists worry that if the Earth's inhabitants continue to use spray cans containing fluorocarbon propellants at the rate they did in 1975, as much as 18 percent of the ozone will be stripped from the stratosphere in the next 50 years.

That would allow enough ultraviolet light to reach the Earth's surface to cause a worldwide increase in skin cancer.

The satellite placed in orbit yesterday by the National Aeronautics and Space Administration carries an instrument called SAGE -- Stratospheric Aerosol and Gas Experiment.

NASA put SAGE into an almost circular orbit about 400 miles up, where it will follow a northeasterly path over 80 percent of the Earth's surface. Each time the satellite encounters the sun rising and setting, the SAGE instrument will measure the ozone and dust layers in the stratosphere.

A telescope aboard the satellite scans the sun as it rises or sets, then scans down across the Earthhs horizon using the sun as a light source for a 'picture' it takes of the stratosphere.

Built into the instrument is an optical filter that breaks down the sun's light into four colors: blue, blue-green, green and near red. Each of the four colors travels differently through key components of the stratosphere.

For instance, the ozone layer near the top of the stratosphere about 28 miles up absorbs most of the green light of the sun.

By measuring the way the sun's light is bent as it travels through the stratosphere, the satellite can measure the components of the stratosphere, including ozone.

The space agency expects the satellite to operate at least one year and possibly as long as five. The longer it works, the more information it will provide on how the ozone might be changing.

At the very least, the satellite will provide clues on where the ozone is being broken down. At an altitude of 28 miles, the ultraviolet light of the sun attacks the spray-can propellants and releases free chlorine believed to cause the most damage to the ozone.

By studying the "aerosol" dust layer just below the ozone, the space agency hopes to develop new ways to predict worldwide climate change. The dust layer is made up of tiny particles of sulfur and sand blown into the stratosphere by volcanic eruptions and desert storms.

The dust in the aerosol layer can form a haze over certain parts of the world, causing a cooling effect that often leads to increases in rainfall. The satellite measurements of the ozone and dust layers will be bolstered in the next year by rocket, balloon and aircraft studies around the world.