LOS ANGELES (AP) _ Cancer deaths from the Soviet nuclear power plant disaster could exceed the short-term death toll from the bombing of Hiroshima, assuming most of the reactor's radioactivity was released, a physicist says.

The amount of radioactive strontium 90 and cesium 137 in the Chernobyl reactor is equal to that produced by a 30-megaton nuclear bomb blast, said Theodore Taylor, who served on the presidential commission that investigated the 1979 Three Mile Island nuclear power plant accident.

A blast that large is 2,000 times greated than the 15-kiloton bomb dropped on Hiroshima, Taylor told a news conference Wednesday sponsored by a Southern California group opposing nuclear energy.

Because of Soviet secrecy, it isn't known how much radioactivity was emitted from the Chernobyl plant, but if most of it was released the resulting number of future cancer deaths might be larger than the death toll at Hiroshima, he added.

At least 70,000 Japanese died within a month of the Aug. 6, 1945, bombing of Hiroshima, and more than 40,000 within a month of the Aug. 9, 1945, atomic bombing of Nagasaki, which ended World War II.

Daniel Hirsch, director of the Adlai Stevenson Program on Nuclear Policy at the University of California at Santa Cruz, agreed with Taylor.

''Potential (cancer) casualties, if there were a major fraction of the (radioactive materials in the reactor) core released, would be on the same order of the number of people who died at Hiroshima and Nagasaki,'' Hirsch told the news conference, sponsored by the Committee to Bridge the Gap.

Taylor and Hirsch emphasized that the future number of cancer deaths depends on many factors in addition to the amount of radioactivity released, including the effectiveness of evacuations, wind patterns and future decontamination efforts.