UPDATE 1-US: Blue Rhino and AmeriGas colluded on propane in 2008

WASHINGTON, March 27 (Reuters) - Two key propane suppliers, Blue Rhino and AmeriGas, illegally coordinated in 2008 by reducing the amount of propane in tanks from 17 pounds to 15 pounds without cutting the price, U.S. authorities said in an administrative complaint filed against the companies.