DETROIT -- Men of action who are men of thought are rare. Edward Vaughn is among the few. He has been an executive assistant to Coleman Young, mayor of Detroit, since 1982. He is the door to Young's office, the hinges of which shake daily because Vaughn's work includes handling all constituent complaints, all police complaints and appearing at all public meetings with Young.

When all the alls are added, Vaughn still has room for another life -- the bookman's. Since 1959, which in Detroit's measurement of time means eight years before the city riot that took 43 lives and destroyed 1,300 buildings, Vaughn has owned and run what is now considered the oldest black bookstore in America. It specializes in Afro-American history, an intellectual passion that Vaughn indulges with regular journeys to West and East Africa.

This afternoon he is in northwest Detroit on Elijah Muhammad Boulevard, explaining the local lay of the land. ''In the middle of this block,'' he says, pointing to a low bulky building set between shops, ''is the mosque where Malcolm X was once minister. That was in the early 1960s.'' The mosque is called Masjid Al-Fatiha. ''That's from the first chapter of the Koran,'' Vaughn explains.

As he tells stories of local heroes -- from Aretha Franklin, whose father was a minister, to Martin Luther King Jr., who was a regular visitor to Detroit's churches -- Vaughn also remembers such black writers as Jean Toomer, Claude McKay and T. Thomas Fortune. He has sold their books for nearly 30 years, becoming sold himself on the belief that passing on black culture to Detroit's young is as important as anything he does politically for the mayor.

Though large, Vaughn's contribution is but a drop of water in the city's deep well of chaos. Motown is now Guntown. Schools are shooting galleries. Fourteen teen-agers were shot and killed over the Labor Day weekend. Forty-three died in 1986, with 365 wounded. This year the death rate has increased 12 percent.

''Drugs,'' says Vaughn, ''are the major problem. If drugs were eliminated, we wouldn't have much of a problem. It's not so much that the kids get hooked on drugs. They sell them. It's a business. This is the first city in America that I know of where kids were brought in to sell drugs. Young Boys, Incorporated, was the organization that started young fellows selling drugs.''

Vaughn didn't learn this by reading reports on ''the drug crisis.'' He saw it through the window of his bookstore, beginning in the mid-1970s: ''I'd look outside and see these young kids I had known some years earlier when they took out trash for us and worked around the store. Next thing I know, they're out selling drugs on the streets.''

The market for drugs, Vaughn discovered, was larger than he imagined: ''I had in my mind a picture of the people buying drugs: the rowdy elements, shady characters. But the buyers tended to be middle-class people, neatly dressed, black and white, driving up and buying drugs from these kids. There is a tremendous market here, and all over the country, for drugs.''

As drug selling increased, book selling decreased. Some years, Vaughn, 53 and raised in Dothan, Ala., had sales of $500,000. When the gross went below $20,000, he went into politics. In 1979 and '80, he served in the state legislature. For nine years before that, he taught African history as an adjunct professor in Detroit universities.

The decline in reading coincided with the onrush of drugs in the mid-1970s. Vaughn recalls that was also the time when schools began to lose interest in the teaching of black history and culture in high schools and colleges. Political erosions were also occurring: ''the moving away by the federal government of programs designed to help the black community. This was happening even before the Reagan years.''

Much of Vaughn's assessment is backed by ''The State of Black Michigan: 1987,'' a report by the Urban Affairs Program of Michigan State University. In education, employment, housing, health and representation of blacks in corporate management and boards, the inequalities of 1987 are similar to the racism and frustration that led to the riots 20 years ago.

In the early 1970s, after Detroit, Watts and other fires were put out, black pride was used as a social force. Edward Vaughn believed in it and built a small business around it. His store, currently closed for renovations, was able to compete in the marketplace against every business but the drug business. When the handguns come out and are fired in the war over drug profits, not only teen-agers are being killed off. Books and ideas are dying too. ". . . not only teen-agers are being killed off. Books and ideas are dying too."