If the trial of Rep. Charles C. Diggs Jr. (D-Mich.) had a dramatic moment, it was the appearance of four prominent civil rights leaders to testify in behalf of the senior black member of Congress.

The testimony of the four - Coretta Scott King, United Nations Ambassador Andrew Young, Detroit Mayor Coleman Young and the Rev. Jesse Jackson - was unqualified in support of Diggs. The endorsement of Diggs honesty and integrity was without reservation. And, according to interviews with several jurors, the testimony of the character witnesses had no effect on the verdict.

"All the jury thought that they were fine people," Bernice L. Davis, a retired Department of Transportation employe, who is black, said of the character witnesses. But, she added "their testimony had no bearing on what he was found guilty of."

Before the jury recessed after deliberating for three hours the first day, the jury had convicted Diggs on 10 counts of mail fraud, according to the jury foreman. By 3 p.m. the next day, Diggs had been convicted on all 29 counts of the indictment charging him with illegally diverting more than $60,000 in congressional employes' pay to his personal use.

At no point, according to jurors interviewed, was there any serious disagreement about the verdict. Nor, according to all acounts, did the question of race - which was addressed obliquely throughout the trial - come up during the deliberations.

Comments Davis and other jurors made indicate the jury considered the character testimony - and the prominence of the witnesses giving it - to be irrelevant to the charges against Diggs.

Jury foreman Leon C. Perry, 31, a student at the University of the District of Columbia and one of 11 black persons on the 12-member jury, said he expected the defense to put on character witnesses "who would be well known - to blacks especially. I wasn't surprised," he said, "but they didn't have anything to do with the case."

The defense in the Diggs trial attempted, for the most part unsuccessfully, to introduce evidence concerning Diggs' work in the civil rights movement and his efforts as chairman of the House District Committee in securing passage of home rule for the District of Columbia and creation of the University of the District of Columbia.

That strategy appears to have fallen on deaf ears. "I was supposed to decide based on the evidence presented in court whether a crime was committed," Perry said. Diggs, Perry said, was "very evasive" as a witness. "I thought he didn't tell the truth at all. I thought he acted like he had something to hide. He wasn't cooperative at all. I was surprised he took the stand.

Perry said it "bothered" him that he was black and Diggs was also. When the time came to vote Diggs guilty, Perry said, "I would have rather I didn't have to do it, but I had to do it because to me it was obvious."

The defense, Perry said, "didn't present much of a case."

When Richard M. Nixon was named as an unindicted coconspirator by the Watergate grand jury in 1974, then-White House aide Patrick J. Buchanan wrote:

"Only a single member of that 23-member grand jury was a Republican. Seventeen of the 23 were black - members of a racial minority that voted, nationally, upwards of 10 to 1 against the president, a minority whose political leaders have repeatedly characterized Richard Nixon and his administration as bigoted and racist."

Former White House aide John D. Ehrlichman, while on trial for his role in the breakin at the offices of Daniel Ellsberg's psychiatrist, had a black lawyer on his defense team. Observers remarked at the time that the lawyer's presence was an attempt to win favor with the predominantly black jury. Ehrlichman, however, was convicted.

One source, familiar with the strategy of the defense in the Diggs trial, said it is "crazy" to think that blacks are more likely to acquit than whites on a jury. Blacks are more distrustful than whites of police, the source said, but not of prosecutors. "There is no question that blacks are more conservative, more law-and-order oriented than whites," this source said.

And Buchanan does not disagree, "Washington," he said in an interview this week, "is a very law-and-order town."