California health officials said yesterday that they found dangerous levels of a widely used toxic pesticide in half of the irrigation and drinking water wells they have tested in a major agricultural area of that state.

Dr. Keith T. Maddy, head of the health and safety unit of California's Department of Food and Agriculture, said that despite a two-year-old ban on the pesticide dibromochloropropane (DBCP) in California, residues from the chemical were found averaging 5 parts per billion in wells tested in the state's giant San Joaquin Valley.

Maddy said the state has recommended that all wells showing more than 1 part per billion of DBCP be closed to human consumption. At that level, he said, the state estimates the contaminated water will cause cancer in one of every 2,500 persons who use the wells.

An Environmental Protection Agency spokesman said yesterday that its science advisory panel would meet June 29 to consider the DBCP data from California and other states where tests are under way. "we would hope to make a decision on what action to take as soon after that as possible," he said.

Arizona health officials said yesterday that similar drinking water tests in an agricultural area near Yuma showed DBCP concentrations of from 4.6 to 18.6 parts per billion in six of 18 wells that were tested.

"we are issuing an immediate recommendation to persons with those wells not to use that water for drinking or cooking and we are asking EPA for more information on on what to do next," said Bruce Scott, assistant director of the Arizona Department of Health Services.

Citing the California figures, the Health Research Group, a public interest organization here, yesterday called on the EPA to impose an immediate emergency ban on further use of the pesticide.

According to Maddy, DBCP is considered a "mid-range" carcinogen. "the problem is that it is more powerful than anything else," he said. "the problem is that it is contaminating drinking water. We drink about two litters of water each day so you get consumption of something containing a carcinogen at about twice the level of the entire daily food diet."

The EPA halted the use of DBCP in 1977 on 19 fruit and vegetable crops after it was disclosed that the pesticide was causing sterility in workers who manufactured it and it caused cancers in laboratory animals.

But the EPA, under heavy pressure from the food industry, allowed the continued use of the pesticide on a number of other crops such as soy-beans, citrus fruits, grapes and nuts. A California official said yesterday that an estimated 10 million pounds of DBCP is used annually in the United States.

In a letter to EPA Administrator Douglas M. Costle requesting the immediate ban, Dr. Sidney M. Wolfe, head of the Health Research Group, said yesterday that DBCP is particularly heavily used in Arizona, Florida, Hawaii, Texas and South Carolina.

"water in those areas," Wolfe said, "is likely to contain even more DBCP than in California where the chemical has not been used for two years."

Maddy said that since California made its recommendation to close wells with more than 1 part per billion of DBCP late last month, a number of communities have shut down their contaminated water supplies. "some of those included new wells that it cost them $300,000 to dig," he said.

DBCP is normally used to inhibit root rot in crops. It is injected into the roots, and agricultural specialist say some of the chemical leaves the ground as a gas and is deposited on the leaves and fruit of plants. California officials said DBCP is the only pesticide they have tested which shows a tendency to absorbed into ground water.

The sole U.S. manufacturer of the pesticide is the Amvaac Chemical Company in Los Angeles. Glenn Wintemute, president of the company, said in a telephone interview yesterday that he did not believe DBCP was either a carcinogen or that it could cause sterility.

Wintemute declined to say how much DBCP his firm produces.