Raha Wala, a 30-year-old lawyer for an international human rights organization, is facing $200,000 in student loan debt. But if all goes according to plan, most of that burden will be forgiven after 2020 under a federal program aimed at helping those who enter public service jobs. “It’s enabling me to do the work that I love,” said Mr. Wala, who graduated in 2010. “It wouldn’t be possible, otherwise.” The federal government is trying to encourage more participation in the Public Service Loan Forgiveness program, which was created in 2007. The program and other debt assistance options have been underused...