EVERYONE WHO follows politics is tempted, from time to time, to try to summarize a politician's entire record in a single word or by a single number. And so one reads that Senator X is a liberal and Governor Y is a conservative. In recent years, almost every organization you can think of has taken to giving numerical ratings to legislators. Some of these ratings are useful, if you keep in mind their limitations; the AFL-CIO, Americans for Democratic Action and Americans for Constitutional Action have for many years produced ratings that cover a wide range of issues and that are based on a consistent, coherent view of what public policy should be. They provide useful information for someone who wants to judge a legislator's record.

But ratings can easily be misleading and misused. A case in point is the rating of presidential candidates on issues by the NAACP. These purport to cover candidates' voting records on civil rights in Congress from 1965 to 1982--although most of the candidates rated did not serve in Congress for most of that time, and two of them--Ronald Reagan and Reubin Askew--did not serve there at all. Moreover, there have not been all that many roll call votes on civil rights issues during that time. Sen. Ernest Hollings has a particular gripe: his rating was a low 39.8 percent, and he thinks that's not a fair test of where he stands now or of what he would do as president on civil rights issues.

The senator has a point. He began his political career in South Carolina in 1948, when the state gave 72 percent of its votes to Strom Thurmond's State's Rights Democratic Party, and he was elected governor in 1958, when segregation was the law in his state. As governor, he saw that desegregation orders were peacefully obeyed--a vivid contrast to many southern governors in those days--and his subsequent record on civil rights and other issues has won him the support of the overwhelming majority of South Carolina's black voters.

The senator's objections point up the limitations of numerical ratings. You can't sum up a human being in a single number. When voters elect a president, they are choosing someone to set a public agenda. To get a sense of how a candidate would do that, you need to understand something of his basic instincts and deep beliefs, his personal character and ideas about the future. These things are, at most, only suggested in a dim way by numerical ratings or, for that matter, by adjectives like liberal or conservative. Ratings are one way to see whether a presidential candidate has followed an orthodoxy in the past. But they are at best only one small bit of evidence of what he would do in the future.