Agriculture Secretary Tom Vilsack announced on Thursday that he would authorize the unrestricted commercial cultivation of genetically modified alfalfa, setting aside a controversial compromise that had generated stiff opposition.

In making the decision, Mr. Vilsack pulled back from a novel proposal that would have restricted the growing of genetically engineered alfalfa to protect organic farmers from so-called biotech contamination. That proposal drew criticism at a recent Congressional hearing and in public forums where Mr. Vilsack outlined the option.

Mr. Vilsack said Thursday that his department would take other measures, like conducting research and promoting dialogue, to make sure that pure, nonengineered alfalfa seed would remain available.

“We want to expand and preserve choice for farmers,” he told reporters. “We think the decision reached today is a reflection of our commitment to choice and trust.”