WASHINGTON – The U.S. Supreme Court on Monday ruled that a federal judge went too far when he banned the planting of genetically engineered alfalfa seeds after claims that the plants might harm the environment.

In a 7-1 vote, the court reversed a federal appeals court ruling that had prohibited Monsanto Co. from selling alfalfa seeds because they are resistant to the popular weed killer Roundup.

The U.S. Agriculture Department must now decide whether to allow the genetically modified seeds to be planted. It had earlier approved the seeds, but courts in California and Oregon said the USDA did not look hard enough at whether the seeds would eventually share their genes with other crops.

“In light of the Supreme Court’s decision to invalidate the lower court’s injunction, USDA is moving forward with the completion of the environmental impact statement on the deregulation of Roundup Ready Alfalfa, and nothing in the Supreme Court’s decision affects that ongoing process,” said Caleb Weaver, the USDA’s press secretary.

“This Supreme Court ruling is important for every American farmer, not just alfalfa growers,” said David F. Snively, Monsanto’s senior vice president and general counsel.

“All growers can rely on the expertise of USDA and trust that future challenges to biotech approvals must now be based on scientific facts, not speculation.”

Opponents of the genetically engineered seeds also claimed victory.

“The ban on the crop will remain in place until a full and adequate EIS (environmental impact statement) is prepared by USDA and they officially deregulate the crop. This is a year or more away according to the agency, and even then, a deregulation move may be subject to further litigation if the agency’s analysis is not adequate,” said Andrew Kimbrell, head of the Center for Food Safety.

“In sum, it’s a significant victory in our ongoing fight to protect farmer and consumer choice, the environment and the organic industry.”

A federal judge in San Francisco had barred the planting of genetically engineered alfalfa nationwide until the government could adequately study the crop’s potential impact on organic and conventional varieties.

St. Louis-based Monsanto argued that the ban was too broad and was based on the assumption that its products were harmful. Opponents of the use of genetically engineered seeds say they can contaminate conventional crops, but Monsanto says such cross-pollination is unlikely.

“We agree that the District Court’s injunction against planting went too far,” said Justice Samuel Alito, who wrote the majority opinion.

Justice John Paul Stevens was the only justice to dissent. “It was reasonable for the court to conclude that planting could not go forward until more complete study showed that the known problem of gene flow could in reality be prevented,” he said.

Alfalfa, which is used for livestock feed and can be planted in spring or fall, is a major crop grown on about 22 million acres in the U.S., Monsanto said in court papers. The U.S. Agriculture Department must now decide whether to allow the genetically modified seeds to be planted.