After a month without a major outbreak of the tenacious Mediterranean fruit fly, California officials have become so confident of victory over the insect that they have ordered an end to roadblocks around infested zones.

Also, despite the possibility of more isolated Medfly discoveries, the California farmers who feared a major agricultural catastrophe now acknowledge that they have brought in a harvest almost untouched by the insect.

"My guess is that we are probably going to see sales 2 or 3 percent over what we sold last year," said Baker Conrad, information director of the Council of California Growers.

The state now has so many Medfly traps, as many as 50 per square mile in some areas, that state officials say they are confident that they can stamp out further small outbreaks quickly.

The last major outbreak, on Aug. 25 in northeast Los Angeles, seems to be under control. Medfly maggots found in a peach tree in the Castro Valley Tuesday were inside the northern quarantine zone, and were not considered a serious threat.

United Press International reported tonight that four Medflies were found today at Los Angeles International Airport. Los Angeles County Agriculture Commissioner Paul Engler was quoted as saying that three of the flies were found flying inside a cargo area and the fourth in a trap. Engler said he was convinced that the flies are sterile, "But we have to wait for confirmation from Sacramento."

Highway checkpoints to stop the movement of infested fruit from San Francisco Bay counties will be gone by Oct. 1, Medfly project spokesman Annie Zeller said, and no roadblocks are planned in Los Angeles.

Daily aerial spraying should also end by mid-November, she said, and not resume unless more flies are found next spring after the insects' winter dormant period.

The end to roadblocks is a significant measure of how far anti-Medfly officials feel they have come. In the past they have blamed motorists carrying infested fruit for worrisome outbreaks of the insect on the edge of California's San Joaquin Valley, the heart of the state's $16 billion agricultural industry, and in Los Angeles.

Aerial spraying of more than 1,265 square miles of the infested zones has so lessened the possibility of infested fruit remaining in the area that it was not worth the heavy cost of continuing the roadblocks, Zeller said.

Besides Tuesday's Castro Valley find, Medflies were found earlier this month just beyond the spraying zone in Milpitas and Pleasanton, but officials said these were minor outbreaks that could be contained.

Local residents also have become far more careful about taking fruit out of the area, so that confiscations at the roadblocks decreased from 1,400 to 300 a day.

No Medflies have been found in the Los Angeles infested zone since Sept. 3, and none in the central valley infested zone near Westley since Sept. 2. A female fly found at Los Angeles International Airport Tuesday was later determined to be sterile and not a threat. Reports on the sterility of today's find at the airport are pending.

Medfly projects manager Jerry Scribner has said he will accept in principle a recommendation by the project's technical review committee that spraying stop after two Medfly life cycles have concluded. The committee estimated that one life cycle lasts 54 days, but Scribner said he thought it may be shorter than that.

According to Zeller, the committee recommendation means that spraying of some infested areas of Santa Clara and San Mateo Counties may end as early as late October or early November.

She said all daily spraying should end by mid-November or when the weather turns cold, and areas that had not yet been sprayed for two life cycles would get a once-a-month spraying through the winter.

The Medfly lays eggs inside more than 200 varieties of fruits and vegetables. The eggs hatch into larvae, or maggots, which eat the fruit and ruin it. Then they drop to the ground and dig in for their pupal stage before emerging as flies.

These pupae can remain dormant underground for several months in cold weather, scientists say, making spraying less effective because the insecticide malathion attacks adult flies.

Conrad, representing California growers, said some farmers located in the mostly residential infested zones were hurt by the insect, "but aside from that, we were hardly affected."

Even inside the infested areas, many farmers were able to sell despite the ban on shipping beyond the quarantine borders. "The cherry crop was small so we were able to sell it within the area. The apricots went to dryers anyway, and after being dried they could be shipped out," he said.

Growers of bell peppers and tomatoes inside the quarantine area suffered some losses. The market for lemons and melons was also hurt when the Japanese, who buy about $118 million in California produce a year, insisted that all state fruit be fumigated before being shipped to them.

State officials have estimated the total cost of fighting the Medfly and its damage to crops at about $100 million this year, but Conrad said it was impossible to determine precisely how much of that was in lost sales and increased fumigation costs.

Vernon Crowder, an agricultural energy analyst with the Security Pacific National Bank, agreed that California produce sales may be higher this year, but noted that last year's sales were poor.

California farmers this year also suffered lower prices for their fruits and vegetables. Crowder blamed this mostly on an overabundant harvest, but also on the Medfly scare and the effect it had on buyers.