As college-access advocates work to preserve federal student-aid funds in a difficult budget climate, it’s natural that most of their attention is focused on Pell Grants. After all, that program provides low-income students with grants that don’t have to be repaid. But Joseph E. Aoun, the president of Northeastern University, is worried that the Perkins Loan program, which provides low-interest federal loans to needy students at participating colleges, is getting lost in the shuffle. And, with that program set to expire in 2014, it is an urgent concern.