Japan announced tonight it will enforce a ban on all California fruits that have not been disinfected despite U.S. efforts to soften the embargo aimed at the Mediterranean fruit fly.

The Japanese decision, announced Wednesday morning in Tokyo, will be a blow to California growers, who count the Asian nation as their No. 1 foreign customer. California sells more than $120 million in fresh fruit to Japan each year.

Anne Warring, a spokesman for the group of California growers known as Sunkist, said the group had already canceled its next weekly shipment of citrus to Japan. Sunkist growers have said, however, they are making preparations to fumigate as much as of their exported crop as they can to meet the Japanese requirement.

California growers in general, however, are not well-prepared for the fumigation or cold-treatment that might be required of more of their produce if the Japanese embargo spreads to other countries and states. A spokesman for the Council of California Growers said last week that his members were equipped to fumigate only 5 percent of their crop.

A team of U.S. officials has been meeting with the Japanese in Tokyo since Saturday in an attempt to persuade Japan to accept a simple certificate that fruit brought into the country was from Medfly-free areas of California. Only 2 percent of the state is under federal and state quarantine because of Medfly infestation.

A spokesman for the Japanese government said the two sides would continue to discuss what kind of disinfectant treatment would be acceptable to Japan and what varieties of fruits might be admitted because they are not susceptible to the flies.

Most other states and foreign governments have so far accepted California produce if it was accompanied by a certificate saying that no Medflies had been found in the counties in which it was picked.

Five Medflies were found in traps in Los Angeles County yesterday, which could indicate a big leap in the insects' invasion. It was not known immediately, however, whether the flies were fertile or were sterile flies released to interfere with the insect's breeding cycle. Tests were to be conducted Wednesday.

Sen. S. I. Hayakawa (R-Calif.) today called for immediate spraying of the entire San Joaquin Valley, the heart of California's $16 billion agricultural industry, in order to stop any further spread of the insect and restore faith in California produce. Up to now, state and federal agricultural officials have ordered aerial spraying with the pesticide malathion over only those areas where Medflies have been found.

Roadblocks have been used to stop motorists from taking infested fruit to Medfly-free areas of the state, but some cars have evaded quarantine checks and given the insect a small foothold on the western edge of the San Joaquin Valley.

A judge in Texas last night delayed a decision on whether to allow that state to impose further restrictions on California fruits, while California and Texas officials discussed how best to keep the insect from spreading. The small fly lays eggs inside more than 200 varieties of fruits and vegetables, producing maggots which eat and spoil the produce.

Three DC4 aircraft sprayed 33,000 acres near Hollister, Calif., this morning, the first use of the aircraft in the widening anti-Medfly campaign. Eleven helicopters are also being used.