Cyberspace, the virtual domain existing within the chips and wires of computer networks, may be the front line of the next big battle. A clash there may not be decisive, but it could be over in less than a second. As to whether the United States is as prepared as it ought to be, the answer appears to be no. According to government and industry experts, U.S. forces are just beginning their learning curve. The message is that it is time to beef up defenses, partner with the private sector, train the work force and educate the public about the dangers the country faces.