The leaders of Washington University in St. Louis have decided that it has a distinction they no longer want: the nation’s least economically diverse top college.

Only 6 percent of undergraduates at Wash. U., as it’s known, receive federal Pell grants, which typically go to students in the bottom 40 percent of the income distribution. The university rejects dozens of qualified low- and middle-income students every year rather than giving them the financial aid they would need.

Now Wash. U. is planning a major expansion of aid, to be announced Friday, university officials say. It will commit to more than doubling the share of undergraduates with Pell grants, to at least 13 percent, by 2020. That percentage is fairly typical today for a college with its resources.

“We feel we have an important responsibility to serve talented people, independent of their background,” Mark Wrighton, the chancellor, told me, noting that his father was an enlisted man in the Navy and that his mother also didn’t go to college. “I’ve lived the life I’d like to encourage for other people.”