California voters this fall will decide a ballot measure that would require labeling of foods containing genetically engineered material. But the Department of Agriculture is already tied in knots over how to deal with the contamination of organic and conventional foods by biotech crops. On [August 27], a USDA advisory panel will consider a draft plan to compensate farmers whose crops have been contaminated by pollen, seeds or other stray genetically engineered material. The meeting is expected to be contentious, pitting the biotechnology and organic industries against each other. The draft report acknowledged the difficulty of preventing such material from accidentally entering the food supply and concerns that the purity of traditional seeds may be threatened. It also cited fears on both sides that official action to address contamination could send a signal to U.S. consumers and export markets in Europe, Japan and elsewhere that the purity and even safety of U.S. crops are suspect. Bioengineered crops dominate U.S. commodities, including 90 percent of U.S. corn. In some states, penetration is all but complete, including 99 percent of the Arkansas cotton crop. Most processed foods contain genetically engineered material. The organic industry said biotech companies should be responsible for containing their own genes and that contamination threatens the right of farmers to choose how to farm.