California officials yesterday ordered grocery stores and fruit wholesalers in that state to destroy all their watermelons in an effort to stop the spread of illness linked to pesticide contamination.

More than 180 people in four western states and Canada have fallen ill because of what state authorities believe are illegal residues of a controversial pesticide called aldicarb, a highly toxic chemical used to control pests in citrus fruits, potatoes, cotton and some grain crops but not approved for use on melons. State officials said another 200 cases of illness in 23 California counties are under investigation.

State authorities in Alaska, Oregon and Washington also have ordered thousands of melons recalled, and Utah and British Columbia have announced voluntary recalls.

The California order will mean the destruction of more than a million watermelons. The rest of the crop -- about 20 million melons -- may be marketed only if the fruit is tested and found free of aldicarb, the state Food and Agriculture Department announced.

The episode has set off a bitter dispute between area farmers and the Union Carbide Corp., which sells aldicarb under the trade name Temik. Growers contend that their melons were contaminated by aldicarb left over from previous crops, even though the pesticide is supposed to degrade in the soil within 100 days.

Union Carbide officials, with support from state and federal officials, say it is far more likely that farmers misused Temik on a crop for which it is not safe.

"I'm not assuming it was a carry-over. I'm assuming it was an illegal application," said state Food and Agriculture Director Clare Berryhill.

In either case, the incident is likely to prompt new calls for an outright ban on Temik. One of the most acutely toxic pesticides on the market, Temik has been under a cloud of suspicion for more than three years, since it started turning up in ground water supplies in Florida, New York, Wisconsin and other citrus- and potato-growing regions.

Although the chemical causes no known long-term health effects, such as cancer, it is acutely toxic in very small doses. Symptoms of aldicarb poisoning include diarrhea, nausea, vomiting and blurred vision. In severe cases, the chemical can cause nervous system damage and death.

Efforts to curb its use have met with strong resistance from farmers, however, partly because it is one of the few remaining pesticides that is effective against tiny root-eating nematodes and partly because of its mysterious ability to enhance the productivity of plants and trees.

Farmers call it a "magic bullet," an insect-killing product that also produces larger, more abundant and more perfectly formed crops.

Because of Temik's unusual properties, Environmental Protection Agency officials said, farmers may be strongly tempted to use it on crops for which it is not approved.

But agency officials also said they are concerned that any attempt to ban Temik as a pesticide would simply result in its being marketed as a fertilizer, over which the EPA has no regulatory control.

The EPA is conducting a special review of Temik, largely aimed at preventing additional contamination of drinking water supplies. But an agency spokesman said the California poisonings are likely to focus additional attention on the question of dietary exposure.

There are no formal standards for Temik in drinking water, but the government has issued a health advisory suggesting that more than .03 parts per million is reason for concern.

The EPA permits much higher residue levels in some food crops, because Temik breaks down into less toxic chemicals when processed or cooked. Potatoes, for example, may contain up to one part per million of Temik.

A Union Carbide spokesman said the residue levels being found in California watermelons range as high as three parts per million -- about three times higher than the EPA allows for any other crop.