A frustrating legal technicality has made defense lawyers who represent indigent clients vulnerable to fraud and identity theft — because the federal government is required by law to send their paychecks in the mail and not through direct deposit. The arrest of a half-dozen identity theft suspects in Brooklyn last week highlighted the problem: Lawyers assigned to federal defendants through a Criminal Justice Act Panel must wait for five- and six-figure checks to come in the mail in a conspicuous envelope that leaves no question it contains a government check. And it will take a literal act of …