The White House on Friday issued an executive order aimed at safeguarding classified information and protecting government computer networks against unauthorized disclosure such as last year’s release of thousands of pages of secret documents by the website WikiLeaks. The order is the result of a seven-month review by the Obama administration. It sought to find a proper balance between security and the need for agencies to share classified information. Under the order, the government will create a special committee to coordinate information sharing and to ensure that agencies that use classified computer networks have greater accountability for protecting information. Each agency would have a senior official oversee classified information and be responsible for safety measures.