Federal officials set up a high-level working group yesterday to study ways to mitigate the possible health dangers arising from the use of a fruit fumigant that could cause cancer.

Because of increased concerns over the danger of the fumigant ethylene dibromide (EDB), the Occupational Safety and Health Administration sent 20 industrial hygienists to Texas, Florida, California and Hawaii, where fruit is being sprayed with EDB to attack larvae of the Mediterranean fruit fly.

That decision was reached after a late Wednesday meeting involving OSHA, the Environmental Protection Agency and Agriculture Department officials.

"We know the federal EDB standard is not strict enough, and we're looking to make the standard much stronger," said Mark D. Cowan, deputy assistant secretary of OSHA's parent Labor Department. "We consider EDB dangerous enough to commit these employes to a 30-day field study and to put our lab to full use."

Meanwhile, in California, officials of the state's Occupational Safety and Health Administration blocked the unloading by dockworkers near Long Beach of 18 truckloads of EDB-treated lemons that were being shipped from Florida to Japan.

That action came after particles of EDB were measured in the back of trucks at levels up to 45 times higher than the state emergency standards. California standards allow 130 parts of EDB per billion parts of air. Between 1,000 and 6,000 ppb of EDB were recorded, according to Dr. Richard Wade, deputy chief of health for the California agency.

The state agency imposed the standard for EDB on Sept. 23 because of concern about dangers to dockworkers and truckers, Wade said. "We found the federal standard much too high and totally uncon- scionable." The federal standard adopted by the EPA and OSHA is 20,000 ppb.

Earlier this week, a top EPA scientist had charged his agency with ignoring a study that recommended a ban on EDB as an agricultural pesticide by July, 1983, after determining that it caused cancer in laboratory animals. The EPA is reviewing the decision to ban the chemical, but allowed EDB's expanded use in California.

Teamsters and the International Longshoremen's and Warehousemen's Union have been refusing to load Japan-bound freighters with EDB-treated fruit or to help in the fumigation.

The supermarket chains of Safeway, Alpha Beta and Lucky Food Stores last Saturday put either full or partial bans on selling millions of dollars worth of EDB-fumigated fruit in their California stores.