WASHINGTON — The U.S. Department of Agriculture said it may take two years to complete an environmental impact study required by an August court ruling that banned planting of bioengineered sugar beets and returned them to regulated status. The department’s Animal and Plant Health Inspection Service said it anticipates making an interim decision on a request for partial deregulation of the sugar beets before then end of 2010. Industry sources said the U.S.D.A. comment raised more questions than it answered about future plantings of bioengineered sugar beets. More than 90% of the 2010 crop was from such seeds and it was unclear if there were enough conventional seeds to plant a full crop in 2011. The court ruling did not affect the harvesting and use of the 2010 crop.