Federal investigators blamed sabotage yesterday for th e derailment of a freight train near Youngstown, Fla., on Feb. 26 that killed eight persons after a car containing chlorine ruptured.

Kay Baily, acting chairman of the National Transportation Safety Board, which is investigating the derailment, said "sabotage was the cause" and that the FBI has been called into the case.

The freight, a 141-car train south-bound on the 81-mile line from Dothan, Ala., to Panama City, Fla., derailed about 3 a.m. Feb. 26 The chlorine car was one of 41 cars that went off the tracks. It split open and a deadly, heavier-than-air cloud of chlorine gas spilled across nearby U.S. 231.

All of those killed were passing motorists in their teens and early 20s. About 70 other people were injured and a total of 3,500 were evacuated from their homes. They began returning yesterday.

According to Bailey and investigators on the scene, bolts and spikes that held two pieces of rail together had been removed and the rail was pulled to one side. The rail was set in such a way that there was nothing the train could do but derail, Bailey said.

Asked if anything other than sabotage might have caused the wreck, she said, "There is no possible way. We obviously checked that ot in every possible way."

A.V.Hooks, president of the Atlanta and St. Andrews Bay Railway Co. - the Bay Line - yesterday offered a $10,000 reward for any person providing information leading to arrest and conviction of saboteurs.

FBI spokesman George Wiskovsky said there were no suspects.

"We are getting a team organized out there," Wiskovsky siad in Jacksonville. "We have asked anyone with information to contact us."

In Washington FBI spokesman Dave Cassens said "there is no information that there is a foreign power involved," a connotation he said could be derived from the use of the word sabotage. There is also no evidence to the contrary, he conceded. "We're investigating what is obviously a major case, with eight deaths," he said.

The safety board investigators were not able to examine the point of the derailment until yesterday, according to board officials. First the chlorine had to be drained from the ruptured car and neutralized and another car carrying propane had to be unleaded. Then tons of steel and metal had to be moved.

"The way the train left the tracks told us originally it was a very unusual derailment," said board spokesman Bob Buckhorn. "When we finally got a look it was pretty clear what had happened."

Markings on the locomotive wheels, on the ties and on the rails - plus the fact that the bolts had been removed from the plates that hold the joint together - led to the conclusion of sabotage. There were no strain marks on the rails, as there would have been were they not pulled apart before the train passed.

It would take one man about 20 to 30 minutes to remove the joint plates and the spikes and move the rail, board officials estimated. A crowbar and wrenches would be required.

It had been six hours since track had been used before the derailment. The engineer of the earlier train has been interviewed and reported nothing unusual.

Bailey said a faulty wheel caused the Feb. 24 derailment in Waverly, Tenn., that resulted in the deaths of 12 people when a propane tank car exploded.

There are about 7,000 derailments a year in the United States. Last year, 11 people were convicted of intentionally derailing trains in violation of federal law, according to the FBI.