Gov. Charles S. Robb today named a 32-year-old Richmond attorney as the first black in Virginia history to sit on the seven-member state Supreme Court.

The appointment of John Charles Thomas, a Norfolk-born partner in the state's largest law firm, Hunton and Williams, was hailed by black leaders as Robb's most significant effort to give black Virginians a role in state affairs that had long been denied them.

"It's getting mighty hard to criticize Chuck Robb," said Michael Brown of the state NAACP, ticking off a list of the governor's other high-level black appointees. "You can't criticize someone who seems to be trying to include all Virginians in all decisions."

The appointment of a young, black lawyer, relatively unknown outside Richmond legal circles, was a blow to conservative Robb supporters who had lobbied on behalf of other candidates, among them an ex-state senator with ties to the state's once-dominant Byrd machine.

Robb announced Thomas' appointment this morning at a press conference, packed with black leaders and other politicians, after reaching a final decision late last night.

The legislature's failure to fill a vacancy on the state's high court, left by the retirement March 3 of Southside conservative and former Byrd organization disciple W. Carrington Thompson, presented Robb with what he called "one of the most important opportunities I will have as governor."

In making his choice, Robb said he looked first for outstanding legal qualifications, but also for experience that would "bring range and breadth . . . a new dimension" to the court.

By late last week, Robb aides said, those criteria began to point to Thomas, a graduate of the University of Virginia with expertise in civil and commercial law and the first black ever to be made a partner at any of the state's major law firms. Robb didn't reveal his choice, even to close staff, until Sunday, after a half-hour interview with Thomas at the Capitol.

The appointment ended a month of speculation, kicked off when the legislature adjourned in late February after deadlocking on two candidates. Thomas' interim selection to a 12-year term, which requires legislative approval, is expected to be endorsed when the General Assembly reconvenes next January, legislators said today.

Robb's choice won praise from members of Richmond's Main Street legal establishment, but the most enthusiastic comments came from the state's black leaders who had pressed Robb to take the historic step and keep faith with the record black support he received in his 1981 election.

"This is reassuring to those of us who had some part in the governor's election," said Sen. L. Douglas Wilder (D-Richmond), Virginia's leading black politician and a key Robb supporter. "I would say that the installments on that investment have been forthcoming."

"It is like a bar has been lifted in Virginia to racial progress," said Richmond City Councilman Henry Marsh. "It is important for Virginia and for the nation."

The Supreme Court appointment caps a record of increased minority representation in state government that, some say, is emerging as a hallmark of the Robb administration.

Robb has named a black majority to the state Parole Board and appointed the first blacks on the Alcoholic Beverage Control Commission and on the state Board of Elections. "In all cases, these are places where blacks can have an impact," said the NAACP's Brown. "These are not tokens."

Standing at Robb's side today, Thomas said he saw his appointment as an opportunity "to bring justice to all our citizens . . . and to step forward and share the responsibility in the governance of the Commonwealth."

There was almost no open criticism of the appointment today, in part because of Thomas' position at Hunton and Williams, a firm with 208 attorneys that was recently ranked as 35th largest in the nation. The reputation of the firm, a pillar of the Richmond establishment, and the respect Thomas enjoys among its senior partners apparently blunted any questions about his legal qualifications.

"I don't even know Mr. Thomas," said Sen. Edward E. Willey, a Richmond Democrat and president pro tem of the state Senate. "But I am sure he is well qualified or he wouldn't be in such a well-regarded firm."

The only outspoken complaints came from advocates of other candidates and from legislators who feel their geographic regions are not represented on the court. "It is difficult to understand how from the one and a half million people in Tidewater, he couldn't have found someone to appoint," said Sen. William Parker (D-Chesapeake), chief backer of ex-state senator and Chesapeake Circuit Court Judge William Hodges.

Both Robb and his staff said they originally had some concern about Thomas' age -- almost half that of some of the current Supreme Court justices and far less than the average age, 53, of the court's last 12 appointees, according to statistics prepared by the governor's office. After some research, Robb's staff was able to come up with a precedent, always a comfort in tradition-conscious Virginia: Spencer Roane, one of the state's Supreme Court's most distinguished jurists, was 32 when he was appointed in 1790.

The final decision -- typical of Robb's style -- apparently was made by Robb alone. "It was a decision he managed pretty much by himself from beginning to end," said an aide, Timothy Sullivan. "This was a case where the governor laid down the ground rules and stayed personally involved at every step of the way."

Some Democrats suggested yesterday that the timing of the announcement was hurried to avoid any link to the results of the racially tinged election in Chicago on Tuesday. "My understanding was that the governor's decision was timed for Monday so he could be on the record, whatever the signals sent by Chicago," said one Northern Virginia Democrat.