JACKSONVILLE, Fla. (AP) _ An insurance comany has classified the space shuttle Challenger as a ''common carrier'' and has decided to pay triple indemnity on a life insurance policy for astronaut Ronald McNair.

McNair and six crewmates died when Challenger exploded after liftoff on Jan. 28.

His mother, Pearl McNair, of Lake City, S.C., bought life insurance on her three sons many years ago from Independent Life and Accident Co. agent R.K. Turner, also of Lake City.

''I knew the family, watched those kids grow up. Mrs. McNair was a schoolteacher, and when I first knew the family they lived in a shack. But as the years went by they kept steadily advancing,'' said Turner.

''Nobody who knew the family was surprised when Ronald became an astronaut. It was something you'd normally expect from that family,'' he said.

Mrs. McNair originally took out small ''weekly-pay'' policies when ''that was the only insurance we sold.'' Later, she purchased bigger policies.

These policies had double-indemnity payment clauses for accidental death and triple indemnity liability if the death came while riding a common carrier. A common carrier is usually defined as a commercial bus, airline or auto.

''We made a special dispensation in this case, deciding to go ahead and pay the triple indemnity under the common-carrier provision,'' said J.F. Bryan IV, Independent Life president.

Bryan would not disclose the amount, saying it was a private matter. He said Mrs. McNair would probably receive a check Monday.

Turner called Independent Life after he saw the shuttle explode on television to begin action for paying a claim.