The U.S. Department of Agriculture is considering imposing restrictions for the first time on where and how a genetically modified crop may be grown, in a move that could eventually affect a wide swath of the farm industry.

The USDA is considering approving the use of genetically modified alfalfa, a forage crop grown to feed livestock, but with limitations aimed at assuring that gene-altered crops don't contaminate fields of non-biotech crops, according to USDA officials. The...