If the government hopes to trim the trade deficit with Japan, it might look in its backyard first. Although U.S. companies dominate the market for office-phone systems and personal computers, Japanese telephones and PCs grace some high-level Washington desks. The Federal Reserve Board and Social Security Administration have Fujitsu phone systems. And some top Treasury Dept. officials, including Assistant Secretary Alicia Munnell, use Toshiba PCs. The agencies say they comply with Buy America rules. "What can you do when [Japanese makers] come in with the lowest bid?" asks one official.