NASHVILLE, Tenn. (AP) _ How does Bill Clinton rate on sincerity and candor? A little bit ahead of George Bush, but that's not saying much, according to one presidential scholar.

Vanderbilt University professor Hugh Davis Graham has an A-F ''veracity scale'' for the candidates and modern U.S. presidents.

Graham, author of ''The Civil Rights Era,'' a book on the Kennedy-Johnson- Nixon presidencies, said Thursday he worked up the scale in response to national focus on Bush and Clinton's character. He based his conclusions on media reports about Bush, Clinton and Perot and historical information on other presidents.

He gave Clinton a C minus, Bush a D and Ross Perot an Incomplete, because he hasn't held elective office.

''I didn't have too much trouble figuring out right away that no one could get an A,'' Graham said. ''If politicians told the truth like citizens would want to hear, they couldn't get elected.''

The top grade was a B. That went to two presidents: Harry Truman, ''a plain-speaking, crusty old original,'' and to Dwight Eisenhower, ''who didn't have to make a lot of promises because he wasn't a professional politician.''

Gerald Ford and Jimmy Carter each got a C. The biggest group fell into the C minus category: ''People who left quite a mark, but part of the price they paid was being shady on the truth,'' Graham said.

They include Franklin Roosevelt, the first modern president for Graham's grades, John F. Kennedy, Lyndon Johnson, Ronald Reagan and Clinton.

Bush drew lower marks because he switched positions on supporting Reagan, ''voodoo'' economics and women's rights, and because of his statements about being ''out of the loop'' on the Iran-Contra affair.

Graham said Clinton ''shows a great deal more consistency and continuity in his fundamental beliefs'' but questioned how forthcoming he has been on his Vietnam draft history and on marital fidelity.

Only one man failed on Graham's grading scale: Richard Nixon.

''I don't think you even need to get into why with the shadow of Watergate,'' he said.

Graham described himself as a Democrat who hasn't been enthusiastic about the party since 1976. He said he will probably vote for Clinton on Nov. 3.