On Oct. 4, 1974, Gov. Mills E. Godwin, a man of rock-solid conservative credentials, named James E. Sheffield to the Richmond Circuit Court. It was the first time since Reconstruction that a black man had been appointed to a court of record in Virginia.

Yet the Sheffield appointment got scant attention outside Richmond. In The Washington Post, the story ran near the obituaries. History had been made in the capital of the Confederacy, but quietly.

Compare that to the fanfare surrounding Gov. Charles S. Robb's appointment of John Charles Thomas, 32, a lawyer who on Monday was sworn in as the first black on the Virginia Supreme Court.

This time the story was front page news everywhere in the state and in The Post. Even The New York Times, an infrequent visitor to Virginia, took note. Justice-designate Thomas later held an unusual news conference to accommodate interview requests.

A Supreme Court appointment is more significant than a lower court judgeship. Vacancies on the seven-member high court are rare: there were none from 1974 to 1980. As plums go, this was the biggest Robb has had to dispense in his first year and a half in office.

Still, the difference in the reaction may say as much about Robb as the appointment itself. A politician with proven celebrity value, Robb has shrewdly projected himself nationally as a southern progressive, at least on race. The image plays well outside Virginia--perhaps better than it does inside. Robb used this appointment to his advantage. Out-of-town reporters were summoned for the announcement; the news conference room was packed with black leaders from around the state, and even the timing was controlled to ensure the appointment would not be linked to the outcome of the Chicago mayoral race.

Back home, the national publicity shifted the debate over the appointment from Thomas to Robb. It was as if Robb, in naming a black Supreme Court justice, had made himself look good by making Virginia look bad. The fact that this was a "first" suggested that, somehow, it should have happened before. It guaranteed the governor a line in history books, and an easy shorthand reference for future political writers, as in, "Robb, the Virginia governor who named the first . . . "

All this seems to have struck a nerve with some Virginians. One Richmond editorial accused Robb of catering to the "Institutionalized Left" of the national Democratic Party--an idea no doubt puzzling to those in the party's left wing who will never be convinced Robb is one of them. A conservative leader said reaction has been mixed because of a perception that the choice was, above all, political.

Was it political? Even Robb aides acknowledge it was, at least in the broad sense of the word. It is obvious that Robb, who won 96.4 percent of the black vote in 1981, owed a debt to his black constituency, a debt he could easily repay, as one observer noted, with the conservative capital he has built during his first 18 months in office.

Politics also played a part in picking a lawyer whose background in corporate law and whose rank at a Main Street Richmond law firm effectively muffled the voice of establishment discontent. To criticize Thomas would be to attack the prominent law firm of Hunton and Williams and, so far, no Virginia conservative has shown any inclination to do that publicly.

It was also political because, as Robb said at the announcement, he was concerned about giving the Supreme Court, historically filled with aging former politicians drawn from the state's conservative establishment, a "new dimension."

Perhaps most significantly the appointment has to be considered political in a state only one generation away from segregated schools, miscegenation laws and overt discrimination at the polls. Those laws were upheld by the court to which Thomas has been named. Few white conservatives complained then that the court was political.

Nor was there much concern about politics when other Supreme Court vacancies were filled. In 1980, for instance, when Judge W. Carrington Thompson, a Southside conservative and the man Thomas replaced, told a reporter: "You don't campaign for the Supreme Court. You let your friends do it."

Maybe Robb was motivated by his desire for national office or by the size of the black vote that elected him. But the issue, say many of the governor's defenders, isn't Robb's motives, but how well Thomas performs.