Single college students under 22 could find it harder to qualify for federal student aid next year under Education Department rules proposed yesterday, while veterans would find it easier.

Under most circumstances, if a student has no dependents, was supported by his parents during his last year of high school and went straight to college, the proposed rule would bar him from being considered financially independent of his parents for all four years of college.

In most cases, independent students have incomes far below those of their families, and thus are more likely to qualify for federal student loan and grant programs.

The proposals, according to their preamble, are designed to reemphasize "the traditional premise of student aid that the student and/or his . . . parents have the main responsibility for financing the cost of postsecondary education."

Students considered financially independent of their parents would not be affected by the proposed rule changes.

But if a single non-veteran student without dependents received more than $750 in financial support from his parents last year, lived at home more than six weeks last year or was declared a dependent on his parents' 1982 federal income tax return, he would not be considered financially independent of his parents for the purposes of student aid programs until the 1986-87 academic year. Under the current rules, students could qualify two years after breaking those financial ties to his parents.

The key changes would be phased in over the next two years, and would be in effect fully for the 1985-86 academic year.