For years, scientists and engineers have been juggling various combinations of acids, steam, bacteria, catalysts and the digestive juices of microorganisms to convert agricultural waste and even household garbage into motor fuel. So far, such alternative fuels have not moved beyond small pilot plants, despite federal incentives to encourage companies to develop them.

But that could be about to change. Officials at two companies that have built multimillion-dollar factories say they are very close to beginning large-scale, commercial production of these so-called cellulosic biofuels, and others are predicting success in the months to come.