After criticizing California's slow battle against the Mediterranean fruit fly, Florida agricultural officials had their own troubles today when a helicopter broke down and delayed the state's aerial pesticide warfare against a suspected new Medfly infestation.

A fourth Medfly was discovered late Sunday about 11/2 miles southeast of a Tampa neighborhood where the first three fruit flies were found last Tuesday. But agricultural officials said they were not surprised.

"In fact, we more or less expected to find other flies," said Earl Graham, assistant chief of the Bureau of Plant Inspection of the Florida Department of Agriculture. "Any time you find three flies in a trap means you'll probably find thousands of others."

The aerial spraying of the pesticide malathion over 16 square miles in Tampa was rescheduled for early Tuesday from another crop-dusting helicopter flown in from Orlando.

Nevertheless, said Graham, "I think we're on top of it." He said that intensive ground spraying of malathion and speedy placement of small cardboard traps last week got Florida off to a head start in its battle to protect its $4 billion annual citrus industry.

Like the ground spray, the aerial solution will contain a protein-based bait to attract Medflies.

Since last Tuesday, when the first three flies were found in a backyard tree in East Tampa, Florida inspectors have placed 100 traps per square mile in the 25-square-mile regulated area. During a daily inspection of these traps, the fourth fly turned up.

Across the state inspectors have laid 12,000 traps, particularly around food warehouses and railroad yards. Road guards stop trucks as they enter Florida to find out where they came from and where they are headed. At the destination, the produce is inspected as it is unloaded wherever possible. Graham estimated that about 45 tractor-trailers of produce are unloaded each day in the state's five largest cities from Jacksonville to Miami.

Medfly infestations in 1929, 1956 and 1962 caused serious losses for Florida citrus growers. The fly's host is citrus and pit fruits, such as peaches, nectarines, cherries, figs and grapes.

Florida has been trying to ban the importation of fruit from California until the insect has been eradicated there. But a quarantine against California produce last month by Florida Gov. Robert Graham was overruled by a federal judge.

Agricultural officials have not yet determined the origin of the first three flies. Federal scientists said the flies were too decomposed to say whether the two males were fertile or sterile, but they were young. The female, who could have laid up to 500 eggs, may have been sterile, they said. The fourth fruit fly found Sunday was a sterile male.

"It is a very serious situation," said Bobby McKown, executive vice president of Florida Citrus Mutual in Lakeland. "Our citrus industry is much larger than California's."

The spraying of malathion has not aroused objections in the Tampa area, which is home to several industries and scattered low-income residents. The pesticide is sprayed in many areas of the state on a regular basis to control mosquitoes.

Agricultural officials said it was fortunate the initial flies were found 15 miles from major orange groves. But some inadvertent spreading of the pest may have already occurred. Katie Brocato, who owns the property where the flies were found, said relatives often came to her house to pick fresh fruit and take it home with them.