The Environmental Protection Agency thinks the pesticide ethylene dibromide may be dangerous because studies have found that it caused stomach cancer in rats and mice.

But Florida grapefruit growers don't see it that way.

Their representatives told the government yesterday that if EDB is banned, they might not be able to sell any more grapefruit to Japan, which now buys about one-fifth of the Florida crop. That would cause heavey economic losses.

The reason is that Japan requires that the grapefruit be free of larvae of the Mediterranean fruit fly and there is apparently no other way to eliminate the eggs except to fumigate the fruit with EDB.

Agriculture Department officials who attended a meeting at the Capitol yesterday said they knew of no effective chemical substitute.

Freezing or heating the grapefruit after picking has proved effective - but it is risky because fruit treated this way often spoils on the voyage to Japan, they said.

That was the dilemna a delegation of Florida citrus growers presented to EPA officials yesterday at a meeting arranged by Rep. Andrew P. Ireland (D-Fla.).

In a study completed four years ago, 90 per cent of the rats and 50 per cent of the mice dosed massively with EDB contracted stomach cancer. The study was performed by the National Cancer Institute. EPA now has EDB on its list of chemical pesticides to review.

Fumigating grapefruit is a minor use of EDB. Mostly, the compound is used as an additive in leaded gasoline. It is also widely used to combat soil insects in tobacco and vegetable crops. But substitutes are available for the agricultural task.

The only state in which consumers buy grapefruit treated with EDB is California, which, like Japan, has a quarantine against the fruit fly. California buys treated grapefruit from Texas at certain times. Japan is attempting to develop a citrus industry and wants to keep out the fruit fly, which can damage the citrus crop.

Edward A. Taylor, general manager of the Florida Citrus Commission, said that 18,000 truckloads of grapefruit destined for Japan had been treated with EDB since 1974 without any reports of harmful effects. Sen. Richard Stone (D-Fla.) said that the Japanese government, which he said has "cautious" standards on chemicals, had approved.

However, Edwin L. Johnson, chief of pesticide programs in EPA, told the growers group that EDB "appears to be one of the most potent carcinogens we've ever looked at."

EPA will decide soon whether to start a final review process, which could lead to the withdrawal of EDB's registration as a pesticide.

Johnson said firms that manufacture the chemical are conducting their own studies to determine whether workers at their plants have suffered any harmful health effects. Also, the firms have agreed to change the labeling on the chemical to indicate that it must be used under controlled conditions.