Nine Southern states, facing a federally ordered cutoff in June of the suspected cancer-causing pesticide Mirex, are expected to ask federal permission to be allowed to use a substitute whose long-term health effects have not been tested, federal officials said yesterday.

The Environmental Protection Agency, which ordered Mirex phased out by June as a weapon against the widespread infestation of fire ants throughout the South, said Mississippi has already requested approval to use a Mirex-based substitute pesticide called ferriamicide in its place.

EPA said that it experts similar requests from Alabama, Georgia, Louisina, North and South Carolina, Texas, Arkansas and Florida. An estimated 190 million acres of the South are now infested with the highly aggressive and crop-damaging ant, EPA said.

Mississippi, the sole manufacturer of Mirex, halted production of the pesticide in 1976 after laboratory tests showed it produced cancers in animals and was fatal to shrimp and crabs. All ground application of Mirex was ended in December and air applications will be halted by June 30.

Ferriamicide, which was produced under federal and state research grants in Mississippi, breaks down far more rapidly than Mirex alone. The new compound, which uses only about half the Morex as the banned pesticide, biodegrades almost entirely within a month compared to a 10-year lifespan for Mirex alone, according to Mississippi officials.

EPA officials said, however, that the Mississippi research results fo not address whether there might be long-term ferriamicide hazards, including possible cancer or gentic damage to humans.

James G. Touhey, the EPA's branch chief in charge of recommending whether temporary approval should be given for the use of ferriamicide, said a decision would be made next month after a study of existing scientific data and the potential economic effects of rejection.