Japanese officials said today they will not accept California fruits and vegetables without fumigation or cold treatment, the first severe international blow to California's $14 billion agricultural industry.

The Japanese restriction, which U.S. agricultural officials are attempting to soften, came as a California state entomologist predicted further outbreaks of the Mediterranean fruit fly in California's rich Central Valley.

Japan imports $80 million annually in U.S. citrus fruits alone, most from the West Coast, and its restrictions could encourage other foreign buyers to follow suit with severe results for California agriculture.

California growers, who provide about half of all American fruits and vegetables, say they do not have the facilities to fumigate or cold-treat more than a fraction of their crop.

Richard Lara, a tomato grower in Westley, Calif., near the site of last week's first reported Medfly outbreak in the San Joaquin half of the Central Valley, said he could personally lose "hundreds of thousands" of dollars if a long-term quarantine hits his area.

William F. Helms, associate deputy administrator of the U.S. Agriculture Department's animal and plant health inspection service, said his department today suggested undisclosed, but less stringent, alternatives to Japanese officials. Vegetables such as ripe tomatoes, he said, "cannot be fumigated at all."

Federal officials have so far enforced a quarantine on 2,375 square miles of northern California, only 262 square miles of that in the Central Valley.

The discovery of 63 fertile flies near Westley, farther from the center of infestation along San Francisco Bay than the flies could have traveled on their own, has convinced state officials that motorists are sneaking infested fruit through roadblocks in defiance of the quarantine.

Donald Richard Fehlman, an entomologist with the state department of food and agriculture, said, "It is my belief that because the infestation has been so long, we will find it somewhere else in the state." He said he was surprised that it had turned up so far only in a small town like Westley at the edge of the valley. He said he expected flies to turn up in valley cities that attracted more automobile traffic, like Sacramento, the capital.

Future infestations could be caught while "they are still small," Fehlman added, because of increased use and checking of fly traps, and eventually wiped out by aerial spraying. He complained, however, that the state remains at the mercy of future Medflies possibly brought in from Hawaii, where the U.S. Agriculture Department is unable to check all baggage of airline passengers departing for the mainland. Many California officials believe that the first fertile Medfly in the current infestation was brought in from Hawaii.

Helms said his department was investigating ways to tighten baggage checks in Hawaii by adding more inspectors, or by training dogs or inventing X-ray machines that could detect hidden fruit.

The U.S. Agriculture Department in July briefly threatened its own limits on California exports similar to those now demanded by Japan, when California Gov. Edmund G. Brown Jr. resisted a plan for aerial spraying of infested areas with the pesticide malathion.

Brown reversed himself and approved the aerial spraying, despite protests of some residents who feared the pesticide would cause nerve or chromosome damage in humans. The Agriculture Department then assisted California in persuading courts to overturn attempts by some southern states to demand fumigation or cold-treatment of all California products.

Hiroshi Fukuda, an economic counselor with the Japanese embassy in Washington, said the restrictions, to begin Wednesday, were intended only to prevent introduction of the Medfly into Japan, which has so far remained free of the insect. He said Japanese law would require a complete ban on the more than 200 varieties of U.S. fruits and vegetables susceptible to the Medfly if any flies were found in Japan-bound shipments.

The small insect lays eggs beneath the skins of fruits and vegetables, and the hatched larvae feed on the fruit, making it soft. State and federal officials figure they must spend $60 million through October, the most ever spent in a Medfly campaign in this country, to stamp out the major outbreak in the southern end of the San Francisco Bay and smaller outbreaks elsewhere.

Even if the insect is eventually eradicated, as most officials expect, the crop losses and costs of temporary local quarantines will reach at least $500 million, according to one state estimate. Widespread quarantines would also raise food prices nationwide.

According to Roy Cunningham, a federal entomologist and Medfly eradication expert based in Hawaii, the insect probably originated in west Africa. By 1800 it was reported in fruit-growing areas of the Mediterranean coast of Europe, and then began to spread to other parts of the world, reaching Hawaii in 1912 and Central America in 1957.

The most widespread infestations in the United States to date have been in Florida in 1929 and 1956, but the California infestation could eventually break the record. About 1,250 square miles were sprayed in Florida in 1956, compared to 648 square miles so far in California.

The latest California infestation dates from last summer, but state officials mistakenly thought they had eradicated it with ground spraying and fruit tree stripping. They did not begin aerial spraying until a month ago