Nine members of Congress, including several representatives of powerful national security committees, have prepared a letter imploring President Obama to press for expanded natural gas exploration and production in the United States -- primarily though the use of an unconventional and contentious technique known as horizontal hydraulic fracturing."As members of both political parties and as citizens in support of your call to get serious about a long-term policy for secure and affordable energy," reads the Monday dated letter from the group, comprised of four Republicans and five Democrats, "we urge you and members of your administration to take a leadership role in encouraging the continued development and utilization of our nation's vast natural gas resources by any means necessary, but most specifically, by unconventional shale gas recovery."Hydraulic fracturing involves the high-pressure injection of a cocktail of water, sand and a variety of chemicals thousands of feet underground to crack open rock formations and stimulate the release of natural gas.