The pesticide endrin was sprayed on Montana wheat fields last spring legally, even though the endrin levels found in game birds there may cause 17 states to cancel hunting seasons, Montana officials said yesterday.

The toxic chemical was used in compliance with Environmental Protection Agency rules to control a potentially disastrous outbreak of cutworms in 200,000 acres of eastern Montana wheat. But ducks, sharptail grouse and Hungarian partridges taken in the area have shown levels of endrin in their fatty tissues, where the chemical concentrates, that are well above the federally accepted limits for poultry.

What this shows is that "even under conditions of proper usage we still have a problem," said Gary Gingery, environmental management administrator of Montana's Department of Agriculture. "Nearly 99 percent of the spraying was according to the labels."

In high doses, endrin causes birth defects, brain damage and death in humans and animals. At nonfatal levels, studies have found that birds "make poor decisions about protecting themselves and eating right," apparently from brain damage, Gingery explained, so that they become easier prey to larger animals. The effects of low doses in humans have not been fully studied.

Endrin is one of a family of long-lasting pesticides that were in fairly common use 10 to 20 years ago but have since been found to have numerous adverse health effects. Two, aldrin and dieldrin, have been banned in this country, while another, chlordane, may be used now only to control termites, and not on crops.

Endrin's use has also been severely restricted, but in certain cases it may still be used on crops.

EPA project manager for endrin George LaRocca said EPA standards require a 45-day period between pesticide application and harvest so the chemical will have time to dissipate and the crop will be safe for human and animal consumption.

"It's a different situation with game animals. You can hardly have a label that says, 'Do not apply when migratory birds are feeding in the area,' " he said.

Environmental groups expressed concern for a possible threat to several endangered species of western birds, including whooping cranes, the bald eagle and the peregrine falcon. "There's a fairly large arsenal of pesticides for cutworm and this was the poorest choice available," said Jorge Manring of the National Wildlife Federation.

Many other pesticides do not persist in the environment as long as endrin, he said.

EPA toxicologist Hank Spencer, who spent four days in Montana last week discussing the problem with state officials, said he saw no specimens containing endrin levels high enough to be unsafe for humans to eat, although "I would never tell anyone to eat endrin if they can get out of it."

Officials collected about 20 birds and found three with more than 0.3 parts of endrin per million parts of tissue, the level at which the Food and Drug Administration takes regulatory action on domestic chickens, Spencer said.

He added that the fat of one duck contained l.2 parts per million although the meat tested at .005 ppm, well below the ceiling.

The Montana Fish, Wildlife and Parks Commission warned hunters to cut the fatty tissue from any grouse or partridge taken in the current season and to eat no more than one every two days.

A decision on whether to cancel the migratory duck hunting season scheduled to begin Oct. 3 will be made when the commission meets Sept. 25, according to agency official Dale Witt. He said he "rather doubted" that the agency might take a halfway stance, allowing hunting but forbidding anyone to eat the birds.

Montana's verdict is expected to influence the decision on whether to allow hunting in 16 other states along the birds' routes.

Those states are Arizona, California, Colorado, Idaho, Kansas, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington and Wyoming.