California's Mediterranean fruit-fly fighters hope to complete the first round of aerial spraying Sunday morning of a 150-square-mile area of infested land with the insecticide malathion.

Nevertheless, some agricultural experts voiced fears that the helicopter attack was too slow and that the Medfly still might spread into California's rich farmlands."Quite frankly I'm very pessimistic we can keep it out," said Dick Rice, professor of agriculture at the University of California-Davis.

Frank Gilstrap, a Texas A&M entomologist and member of the state Medfly advisory committee, gave the spraying a 50-50 chance of success.

The words of pessimism came after five southern states declared a quarantine on unfumigated California fruits, starting Monday.

California's food and agriculture director, Richard Rominger, said he hoped those states, Alabama, Florida, Mississippi, South Carolina and Texas, would relent when better informed about his state's situation. If not, he said, California growers will go to court Monday in Texas.

California Attorney General George Deukmejian said he would ask the U.S. Supreme Court to stop the quarantine on grounds that it put "an unreasonable burden on interstate commerce." He said he would seek a temporary restraining order.

Meanwhile, Sen. S.I. Hayakawa (R-Calif.) sharply criticized Gov. Edmund G. (Jerry) Brown Jr. today, saying that the Medfly infestation was not an act of God, but "an act of Jerry Brown."

Brown, a Democrat, is considered a potential challenger for Hayakawa's Senate seat next year.

Hayakawa said he recommended aerial spraying in February, but that Brown "sat on his hands, unable to make a decision for months."

The helicopter forays, which began Tuesday, were plagued with spray nozzles that kept clogging with malathion-coated syrup, but technical problems were minimized gradually.

A second round of spraying is scheduled to start next week, when state officials will get their first clue as to whether they are winning or losing the battle against the Medfly threat to California's $14 billion-a-year agricultural industry.

Some fertile flies, given their life cycle, should start turning up in thousands of traps in the quarantined area in spite of the spraying. The clue will be how many are found.