LOS ANGELES, NOV. 5 -- Southern California officials declared victory today in their most expensive war ever against the Mediterranean fruit fly, but joined their bitterest critics in predicting the creature would be back.

After spraying 52,640 gallons of the pesticide malathion over 536 square miles of some of California's most densely populated suburbs, agriculture officials said they had found no significant outbreaks of the tiny pest during warm weather when breeding is most rapid. "We have won this particular battle," said Los Angeles County agricultural commissioner Leon Spaugy, "but all of us recognize there is still a problem of transportation of the medfly into the county."

One member of the state's medfly science advisory panel, University of California at Davis entomologist James R. Carey, was even more pessimistic. "We have eliminated the problem, but not the pest," Carey said. Despite the absence of major outbreaks this summer, Carey said, he still believes there are small pockets of medflies in Southern California ready to burst forth under the right conditions.

In July, when agricultural officials ended 100 nights of helicopter spraying, they expressed confidence they had beaten the pest and could rely on the release of sterile medflies to complete the eradication. More than 5.8 billion sterile flies were released to inhibit the fertile medflies' ability to reproduce. Officials said today they were better equipped to handle future infestations because of a new Hawaiian facility for producing sterile flies.

The end of the $52 million eradication campaign was a boon to the Republican gubernatorial candidate, Sen. Pete Wilson, who supported the spraying despite thousands of complaints from residents of headaches, illness and harm to pets and automobile paint. His opponent, Democrat Dianne Feinstein, had called for an end to spraying, a position that might have won her more votes if the program had continued until the election.

Adelaide Nimitz, a Burbank actress serving as president of Families Opposed to Chemical Urban Spraying (FOCUS), scoffed at the state's declaration of victory, scheduled to be announced formally at a Thursday news conference. "It is not the first time they say they have taken care of the problem," she said.

"We feel they stopped because Pete Wilson didn't want it to be a campaign issue," she said. "We think they'll resume spraying right after the election."

Spaugy said Nimitz was "really grasping" and insisted there was no partisan reason for the spraying schedule. Wilson spokeswoman Lynda Schuler said if there had been a political motive, "they would have stopped the spraying at the height of the political fallout" last winter and spring.

The Southern California infestation did not spread as far as a medfly outbreak in Northern California a decade ago, but it produced at least as much political turmoil. That included a series of local ordinances and lawsuits -- all unsuccessful -- designed to stop the spraying. Isi Siddiqui, the state food and agriculture department official who headed the eradication effort, said he was pleased that an independent panel studying citizen complaints about the spraying "has so far found no adverse health aspects."