Their offices are just four floors apart in Detroit's City-County Building. Mayor Coleman Young is on the 11th floor and Wayne County Executive William Lucas, who recently switched amid much publicity to the Republican Party, is on the 7th. The symbolism is apt: the county government is small potatoes next to the city's, and Coleman Young is by any measure the dominant political figure in the Detroit area. Everyone assumes he will be mayor as long as he wants, and as mayor he gets away with whatever he wants. City employees last month were handing out fliers in the parks inviting the public to the riverfront for the mayor's birthday.

Yet in the long run and the national perspective Lucas may turn out to be the more important politician -- maybe as the nation's first black governor in 1986. The contrast between the Republican on the seventth floor and the Democrat on the 11th is as vivid as their personal relations are perfunctory. "I very seldom see him," Lucas says of the mayor. "I'm in early in the morning." Lucas wants you to know right out that he is a straight arrow, and that Young is not.

Lucas is a teetotaler, a deeply religious Catholic; "I do not use profanity." His parents came from St. Maarten and the British West Indies, and he still has the lilt of the West Indies in his speech; he retains as well a sunny temperament that strikes one as odd in a man who grew up at 137th and Lenox in Harlem. Like Los Angeles Mayor Thomas Bradley, he went to college on an athletic scholarship; he was an interscholastic champion in the mile and cross-country races, contests that require discipline and strategy as well as physical talent. From there he went to the New York Police Department -- "not the most hospitable place, but a chance for a man with a college degree to take exams and get ahead on merit." He was a patrolman on Willis Avenue in the South Bronx and a plainclothesman in Harlem; he went to Fordham Law School at night. A chance encounter at graduation with the speaker, Robert Kennedy, and his press secretary, Ed Guthman, led to a job with the Justice Department in Washington. Then, after President Kennedy was killed, the Civil Rights Division "shut down," and Lucas went to work for the FBI. "It was a good job in law enforcement; there weren't that many blacks in the bureau; I applied and was accepted."

In those years when William Lucas was working his way up through mostly white -- and often hostile -- institutions, Coleman Young had been up, down and then back up in the hurly- burly of UAW and Democratic politics. He came to Detroit as so many other Alabama blacks did in the 1940s and was active in the United Auto Workers; he became a staffer under the regime of R. J. Thomas, whom Walter Reuther accused of being communist- backed and beat in the union election of 1947. At which point Young went back to the line. Not until 1961 was he elected to public office -- delegate to the state constitutional convention, a post that conveniently had no incumbent and from which he was elected from a small inner- city district. He won his seat in the state senate in 1964 thanks to redistricting.

In Lansing, Young became known as a raucous good-timer and as a darned good legislator, a man who could push through a bill on the floor of the Senate in the afternoon and could defend himself with his fists in a bar at night. Once a rebel and still to the left, he was happy to become part of the establishment. When the Democrats looked around at the rubble of their party at Chicago in 1968, they noticed that there were hardly any blacks on the Democratic National Committee. Coleman Young had lined up support from the UAW, other blacks and the incumbent, Neil Staebler, and has been Democratic national committeeman ever since.

Young has deep roots in Detroit, and when he ran for mayor in 1973, he won easily over a white police commissioner; he will win a fourth term this fall. He has always run in black-majority constituencies. Lucas, in contrast, came to Detroit in 1966 as an FBI agent, was named undersheriff in 1968 and elected sheriff in his own right in 1970; he was elected county executive, a new post, in 1982. He has always run in white- majority constituencies. Young has had his problems with rumors of scandal; Lucas is squeaky clean. Young plays ball with the local and national powers that be and prides himself on using politics to get federal money for Detroit; Lucas is unyielding with other politicians and is most proud of gutting the patronage-heavy road commission and privatizing the county hospital.

Young says he doubts that any black could be elected governor, and he knows that white suburbanites, who outnumber Detroiters 2-1, hate him even while they respect his competence. Lucas plainly wants and expects to run for governor next year, and almost no one doubts that's one of the main reasons he switched parties.

He's not a sure winner: incumbent James Blanchard is popular, and Lucas lacks a convincing answer to the question: what would you do that he isn't doing? Lucas does have his own issues -- more prison space, lower taxes to encourage jobs -- but is scrupulous enough to concede that Blanchard's record on these is not completely bad. Moreover, Lucas' current job has limited responsibilities, and he has not been tested on a broad range of issues.

Yet he does have obvious political assets. White suburbanites who are hostile to black politicians understand quite well the contrast between Young and Lucas. Blacks do too, but Lucas can scarcely avoid getting more black voters than the 5 or 10 percent other Michigan Republicans have. Michigan has been so shaken by the collapse of the auto industry and the transformation of its economy that it has been set loose from its old Democratic moorings. Whether he runs, and how he stands up under close scrutiny, have yet to be seen. For the moment he sits four floors below Coleman Young. But he, and not Young, may prove to be the wave of the future for black politicians.