Among the 2,000 students who will graduate from Howard University in ceremonies today is former Michigan representative Charles C. Diggs Jr., who served a prison term for mail fraud and falsifying payroll records but now says his problems are behind him.

Diggs, 60, is receiving a BA degree in political science from Howard's "University Without Walls," a program directed at older, independent students who are unable or unwilling to attend regular classes. A 12-term congressman before he was sent to prison, Diggs received three honorary law degrees over the years. However, his undergraduate education was interrupted by a stint in the Air Force, and he never finished college.

"I've always coveted an earned degree," Diggs said in an interview this week at his apartment in Hillcrest Heights, where he now lives with his fourth wife, Cindy.

Diggs, once the most powerful black member of Congress, resigned his House seat in disgrace. It would seem natural to think of Diggs' graduation from Howard as a kind of fresh start, but Diggs resists the suggestion, maintaining he has nothing to be ashamed of.

"I don't think I lost a lot of ground," he said. "My legal problems . . . . are all in the past. I maintained all along that I did not knowingly violate the law. My conscience is clear."

Diggs, whose family ran a large funeral home business in Detroit, says he plans to open a "first class" funeral home in Prince George's County. He says that he is helping organize a black political convention in the county, and that he has hopes of eventually going to law school.

Diggs, a founder of the Congressional Black Caucus, resigned from Congress in 1980 after being convicted of 11 counts of mail fraud and 18 counts of falsifying congressional payroll forms. The charges involved receiving $66,000 in kickbacks by inflating the salaries of several of his staff members and having them use the extra money for Diggs' own expenses.

Diggs served seven months in a minimum-security federal prison facility at Maxwell Air Force Base in Alabama--a "white-collar" prison, he called it--where he was the editor of the prison newspaper, "Hard Times."

Diggs was released in late 1980 and transferred to a District of Columbia halfway house, where he stayed until February 1981. His period of probation ends next month.

"What has sustained me most is the support and understanding from the black community," he said. "It has offset what might have been a demoralizing experience."

Diggs entered the University of Michigan in 1940 at the age of 17. After a year he transferred to Fisk University, and a year later he was drafted into the Air Force. After leaving the service, he attended a school for undertakers and then took over the family's business in Detroit. About five years later, he ran a successful campaign for the Michigan State Senate, launching his long political career.

Diggs and his wife Cindy were married last month. He has six children from previous marriages, none of whom live with the couple in their three-bedroom apartment.

"God willing, I hope to have another child," Diggs said. "I've had children by every wife."

On a white wall stretching the length of the apartment's hallway are dozens of plaques and pictures that serve as reminders of his past. The burly, bespectacled Diggs says he is proud of awards he received as chairman of the House District Committee, for spearheading efforts to grant the District its home rule charter, to create the University of the District of Columbia and to declare the Frederick Douglass home in Anacostia a national monument.

"They do bring back memories, oh yes," Diggs said of the mementos. "It was a great experience and an honor to be a member of the House for a quarter of a century."

Diggs said he decided to complete his undergraduate education shortly after he got out of prison. At Howard, he completed a two-year program in the "University Without Walls," a nontraditional school that allows a student to work individually with professors instead of attending classes. The bulk of the work involves participation in seminars, reading books and writing papers.

The program gives students college credit for their work experience. Howard officials said that students in the program are not graded, but their performance is evaluated as satisfactory or unsatisfactory.

Diggs said that in his two years at Howard he particularly enjoyed studying the writings of Plato and Aristotle. He said he also studied the origins of black slavery, the evolution of black political movements and the history of African liberation.

In several cases, he said, books he was assigned to read mentioned his name.

Of his plans to establish a funeral home in the county, Diggs said, "It's an undeveloped area--one of the only places in the country where there is a large cluster of blacks with no black mortician. Blacks live here, funeralize their dead in D.C. and then bring them back here for burial. I hope to change that."

Diggs was at first denied an apprentice mortician's license by the Maryland Board of Morticians, but was granted the license last year when the courts intervened.

Diggs said he also plans to become more active in county politics. Black power in the county is dormant, he said. "We want black political empowerment to be as effective as possible in 1984."