Aug 25 (Reuters) - A group of global biotech crop companies won a court victory on Monday that blocks enactment of a law passed last year limiting the planting of biotech crops and use of pesticides on the Hawaiian island of Kauai.

U.S. Magistrate Judge Barry Kurren of the U.S. District Court in Hawaii ruled that the law passed in November by local leaders on the island was invalid because it was pre-empted by Hawaii state law.

The Kauai law required large agricultural companies to disclose pesticide use and genetically modified (GMO) crop plantings while establishing buffer zones around schools, homes and hospitals to protect people from exposure to pesticides used on the crops.

The measure had broad support on the island and the U.S. mainland from organizations and individuals who say heavy pesticide use by the agrochemical companies is poisoning people and the environment.

But in his ruling, Judge Kurren said county leaders on Kauai could not attempt local regulation, agreeing with arguments made by DuPont, Syngenta, Agrigenetics Inc, a company affiliated with the Dow AgroSciences unit of Dow Chemical Co, and BASF.

“This decision in no way diminishes the health and environmental concerns of the people of Kauai,” the judge wrote in his ruling. “The court’s ruling simply recognizes that the State of Hawaii has established a comprehensive framework for addressing the application of restricted use pesticides and the planting of GMO crops, which presently precludes local regulation by the county.”

The law was to take effect Aug. 16, but enactment was delayed pending a court decision after the seed and chemical companies filed suit in January. It is one of a growing number of local and state efforts across the United States to limit the expansion of GMO crops and the chemicals used on them.

Gary Hooser, the Kauai County councilman who introduced the law, said he and others would appeal Monday’s ruling. There was no immediate comment from Syngenta, Dow, DuPont or BASF.

“This issue is far from over. Just another round,” said Hooser. “One ruling by one federal magistrate does not resolve the issue.”

The Hawaiian islands are a popular testing ground for biotech crops for many companies because of their favorable year-round climate. Syngenta, DuPont and Agrigenetics lease thousands of acres on the island for GMO crop testing and other work on genetically altered corn, soybeans, canola and rice.

The companies assert that biotech crops are essential to boost global food production and improve environmental sustainability. And they say the crops and the pesticides used on them are safe and already well regulated by state and federal agencies.

But critics say the crops and chemicals used on them are harmful to people, animals and the environment. (Reporting by Carey Gillam in Kansas City; Editing by Tom Brown)