Rail tank car derailments near small, towns in southeastern Ohio, central Arizona and eastern Pennsylvania forced nearly 1,500 people to spend yesterday away from their homes.

About 750 persons were evactuated when nine chemical tank cars derailed yesterday near Millfield, Ohio, and 500 to 700 residents of Buckeye, Ariz., were forced to leave their homes as cleanup work began from a wreck Saturday that left two propane tankers off the tracks.

One car carrying a flammable liquid caught fire when a Conrail freight derailed yesterday near Feasterville, Pa., and police briefly evacutated residents living within a half-mile of the rural crash site 30 miles north of Philadelphia.

Most of the evacuees from Millfield returned to their homes last night, but about 30 were still being kept out of the area. The Buckeye evacuees returned home late yesterday.

The chemical toluene diisocyanate (TDI) was aboard one of the nine tankers on a 35-car Conrail freight train that went off the tracks about 10 miles north of Athens, Ohio officials said.

Another car contained diphenlmethane diisocyanate (MDI), also flammable and toxic, and officials feared it would rupture if it were moved.

In the Arizona wreck, officials said vandals may have thrown a switch that caused six cars of the 104-car Southern Pacific freight to derail.