Passport Denial Program

I need a passport for my employment but cannot get one because my arrears are greater than $2500. I am in arrears, alledgedly for $25K , due to the original support order which was based on my 1992 income and three children. In 1995 my income was significantly reduced when I left full-time military duty. My case was referred to Child Support Enforcement and the court continued the original support order "based on potential earnings" (as stated by the magistrate). Subsequently support payments were made through court ordered income assignment of 38% of my income, which was less than the support order. That is when arrears began to accrue. Due to the unfortunate death of my oldest child in 1999, my order was reduced but not until 2001. The new order also included additional payment for arrears. In March 2006 my son reached 18 years of age but my support was not reduced again until August 2007. My support ended in September 2007 when my youngest child reached 18 years of age but I continue to pay arrears through income assignment. What can I do to dispute the arrears? Can the support order be modified retroactively? What can I do to obtain a passport?