USCIS.gov: 

Continue to Use the Current Form N-400, Application for Naturalization

Until further notice, applicants should continue using the March 22, 2012, edition of Form N-400 currently available on the forms section of www.uscis.gov. This form should continue to be used even after the OMB control number expiration date of March 31, 2013, has passed. Additional acceptable editions of the form, as indicated on the form page, may also be used. USCIS will provide updated information about the new version of the Form N-400 as it becomes available later this year.