A teen-aged girl was hospitalized for observation and 22 other passengers were treated for minior injuries after an Auto-Train bound for Lorton derailed early yesterday near Florence, S.C.

The derailment forced Auto-Train Corp. to cancel its Friday afternoon train from Lorton to Sanford, Fla. but regular daily service is scheduled to resume today, according to Richard Goldstein, senior vice president of the Washington-based railroad.

Goldstein said preliminary reports indicated an axle on one of the two engines broke as the train was pulling into Florence for a regular stop.

Eighteen of the 22 passenger cars left the tracks. None of them over-turned, but five were "heavily damaged" when they jack-knifed together, he said. The 21 box cars carrying the automoibles were not damaged, he said.

Except for a young woman identified as Maohu Mehtani, 14, of Roslyn, N.Y., who was hospitalized over night, the estimated 500 passengers were taken to Lorton in buses.

Yesterday's accident was the third major derailment by an Auto-Train and the first in which passengers were injuried. About 60 automobiles were damaged in March 1976 when several auto-carrying cars derailed near Lorton: 20 cars were damaged when the auto-carriers went off the track in May 1976 near Jarratt, Va.

Florence police Sgt. Richard Moore, who helped rescue passengers from the derailed train, told United Press International "there were some problems getting the people out" of the badly damaged cars. "The people were trapped inside and it took some time to get them out," he said.

Goldstein said there was no final estimate of the cost of the damage, but said it was expected to be low enough that the company would not file a claim on its insurance, which has a $500,000 deductible.

Previous derailments have caused severe financial problems for Auto-Train Corp., not only because of their cost but also because they were followed by a fall-off in business.

The earlier accidents were blamed by federal investigators on cracks in wheels of the auto-carriers used by Auto-Train. After the last accident in May 1976 the company began a massive maintenance and inspection program.

Goldstein said the broken axle believed to have caused yesterday's derailment was blamed on a bearing failure and was not related to the cause of the previous accidents.