The two companies, Mycogen on Moloka'i and Pioneer Hi-Bred on Kaua'i, failed inspections by the U.S. Environmental Protection Agency, which oversees the companies' test plots of genetically modified corn in Hawai'i. The EPA plans to file formal complaints against the companies by Aug. 30, the agency said in letters to the companies dated Aug. 5.

Officials from Pioneer, a subsidiary of DuPont Chemical, and Mycogen, a subsidiary of Dow AgroSciences, could not be reached for comment.

Officials at the Center for Science in the Public Interest, a Washington, D.C.-based consumer health advocacy group, said the EPA's findings are troubling in that Mycogen and Pioneer, both large-scale and experienced biotechnology companies, are putting consumers and the environment at undue risk.

"The danger is that the pollen from these crops could get out into the wild, into the environment, or into the food supply," said Gregory Jaffe, head of the center's biotechnology project. "We have nothing against genetically modified crops that are approved as safe to eat. But it's very disturbing that biotechnology companies would be doing field test experiments that don't meet the conditions needed to ensure safety for the environment and public health."

The EPA said Pioneer planted genetically modified corn at an unapproved test site at its Waimea Research Center on Kaua'i. The corn is altered to produce its own pesticide that fights corn rootworm, but has not been approved for use as a food crop.

Pioneer also planted the crop too close to other types of corn that have already been approved for use, the EPA said. Pioneer was supposed to leave a quarter-mile gap between the experimental crop and its other crops, far enough away to keep the plants' pollen from mingling.

On Moloka'i, Mycogen failed to use proper tree and plant barriers that would help contain its genetically modified corn pollen, the EPA said.

Jaffe says the EPA's action against Pioneer and Mycogen suggest the federal government is paying more attention to big companies' biotechnology experiments in Hawai'i, which has become one of the world's top test sites for genetically modified crops.

Major agricultural firms for years have planted these crops in small plots in Hawai'i, which is viewed as an ideal place for genetic experiments. The Islands' geographic isolation and mild climate provide a good planting ground with a low risk of contaminating other crops ­ unlike breadbasket states like California or Illinois.

In recent years, companies including Pioneer have also increasingly used Hawai'i as a spot to grow out "parent crops" of government-approved, genetically altered corn and other crops. These seeds are then distributed to farmers worldwide. The danger of contamination by un-approved modified corn, Jaffe said, is higher than if the experimental corn were grown in isolation.

Genetic modification of food crops is considered the wave of the future in agriculture. Companies are not only modifying crops to enhance taste, size, color and flavor, but are also trying to increase yields by making crops that are resistant to drought or pests. Others are trying to make disease-fighting plants: One experimental corn crop recently planted in Hawai'i is designed to produce human hormones that fight herpes.