California's Mediterranean fruit fly, instead of raising food prices, may be helping consumers by accelerating a sharp nationwide drop in the cost of fresh fruit.

California's farmers and grower association leaders blame fear of maggot-filled fruit in part for the recent fall in the prices of pears, grapes, peaches, nectarines and other fruits, as much as a 45 percent drop in some Washington, D.C., area stores.

"We know the Medfly is having a psychological effect on the marketplace . . . people see fruit with maggots in them on TV and that kills demand," said Mickey George, who grows peaches, plums and nectarines in California's Tulare County, located in the southern section of the San Joaquin Valley.

The state, which produces about half the nation's fruits and vegetables, has so far avoided a total quarantine that would, economists say, undoubtedly raise food prices nationwide. Instead, California farmers are trying as usual this time of year to sell a huge harvest.

The growers acknowledge that prices always drop as summer harvests hit the market in August, "but it's bigger this time than you would normally expect," said Baker Conrad, information director for the Council of California Growers. He said wholesalers had told him of considerable resistance to California fruits in eastern markets.

Don Vaillancourt, Grand Union's vice president for corporate communications and consumer affairs, said his chain's prices for pears dropped from 89 cents a pound in mid-July to 49 cents a pound, a 45 percent decline. Grapes dropped from #1.49 to 88 cents a pound and peaches form 59 to 49 cents a pound.

According to data provided by the U.S. Agriculture Department's economic research service, prices at shipping points for seedless grapes fell 19 percent, for pears 11 percent and for peaches 33 percent from the week of July 25 to the week of Aug. 8.

Both Vaillancourt and an economist at the research service disputed California grower's contention that the Medfly crisis had caused the price slump, although both sides acknowledge it is difficult to identify all the factors that affect prices.

Conrad said a decline in carloadss of fruits shipped to the East convinced him that eastern resistance was driving down prices paid to California farmers.

The Medfly infestation has led the federal and state governments to enforce a quarantine on 2,374 square miles of northern California. The insect first made headlines nationwide July 10 when the federal government threatened a statewide quarantine if California did not start aerial spraying of the infested area.

California Gov. Edmund G. (Jerry) Brown Jr. reversed himself and allowed the spraying of the controversial pesticide malathion over heavily populated suburbs beginning July 14. Since then newspapers and television news have carried regular accounts of the spread of the pest around the southern end of the San Francisco Bay and to a small foothold in the San Joaquin Valley.

A five-county, $58 million effort to stop the insect has led to quick spraying over newly infested areas. The fly's advance appears to have halted this week, at least temporarily, but farmers do not think that message has gotten to shoppers.

"People are afraid they are going to have maggots in the house, and that just isn't true," said Conrad. No fruits or vegetables, he noted, may leave the quarantined areas where the Medfly has been found unless they are fumigated or cold-treated.

Conrad said the fall in prices has so worried the commodity groups that control California fruit production that several meetings are planned in valley cities next week. "We want to see if we might put on an ad campaign in the East" to counteract the impression that California fruit is spoiled, Conrad said.

In the Washington area, Safeway Stores reported prices of Bartlett pears dropping from 89 cents to 50 cents a pound and grapes from $1.29 to $1.09 since mid-July. Public relations manager Larry Johnson said nectarines increased from 59 cents to 69 cents a pound and peaches from 25 to 39 cents a pound, noting the July peach price had been a special.

A Giant Food spokesman said they kept no record of their July fresh fruit prices for comparison.

In the anti-Medfly campaign, state officials said 11 helicopters sprayed a record 209 square miles last night. This included 17 square miles around the east bay town of Newark, where two new fertile flies were found Wednesday. Newark is outside previous spraying zones but inside the quarantine area, so the new flies did not represent a significant Medfly advance.