MAKING HISTORY, Gov. Robb has appointed John Charles Thomas, a young and talented black man to the Virginia Supreme Court. In every apparent way, the selection of Mr. Thomas is a progressive step for the state, as well as solid evidence that Mr. Robb's commitment in 1981 to "acting affirmatively" is serious. It has taken longer in Virginia than in other states of the South for this kind of progress. But the choice of Mr. Thomas, 32, is more than an addition of color and youth to the state's highest court. He also brings experience and the high regard of his colleagues at the bar.

"My first consideration," said Gov. Robb, "was absolute qualification." He based his decision on recommendations of other judges and lawyers and on a reading of Mr. Thomas' briefs, finding them "well-reasoned, well written and very professional." Recently made a partner in a top Richmond law firm, Mr. Thomas was a member of an honor group at the University of Virginia Law School and has performed corporate and civil work.

That would be enough, but the appointment of Mr. Thomas to the court does, as Gov. Robb noted, add a "new dimension" to this court. It recognizes that black people in Virginia, who comprise about one-fifth of the state's population, do make a difference in politics and can make the state's highest officials more responsive to their interests. For too long, that wasn't so. But Gov. Robb seems determined to make state government more representative. A strong confirmation by the legislature of this latest action would underline the importance of this historic occasion for Virginia.