Outside the Capitol last week, standing on the steps in the summer sunshine for all the tourists to see, was a familiar political sight --a member of Congress greeting and being photographed with a group of constituents. The politician went down the line, shaking hand after hand. Hardly worth noting, except that it underscored an overwhelming political fact. That particular scene would never have occurred not so long ago, for all the visitors were black and the politician was Sen. Strom Thurmond of South Carolina.

Nothing demonstrates better the political power of the ballot -- and of the racial revolution that culminated in the Voting Rights Act of 1965 -- than that sight of Strom Thurmond courting blacks on the Capitol steps and then joining other Deep South senators in supporting the constitutional amendment for the District of Columbia.

When the Senate roll call had been completed, guaranteeing passage of the D.C. voting rights amendment, a singular fact was clear: it could not have been accomplished without the backing of key representatives from the Old Confederacy states. Senators from Georgia, Alabama, Florida, Arkansas and Texas joined the delegation from South Carolina.

But it was Thurmond's action, symbolically and literally, that showed how much the nation has changed. It was Thurmond who led the Dixiecrat revolt against the Democratic liberals and Harry Truman in the dramatic year of 1948.It was Thurmond, when the conservatives finally had their day at a national convention and got their ideological choice who dramatized that political upheaval by renouncing his Democratic Party membership and becoming a "Gold-water Republican" in 1964.

During that rancorous presidential campaign, when Thurmond's role and inflamed tensions over race delivered South Carolina for the first time to the Republicans. A shrewd Democratic politician there ventured a prohecy.

"Two years from now," he said, "Strom will have to run for reelection against a Carolinian and he is going to have to moderate his views on issues affecting the state if he hopes to win the votes of the cotton workers, the defense workers, and the business community. And he is going to have to moderate his views on blacks, because as sure as I'm sitting here they are going to be voting in great numbers some day soon and Strom is going to need their votes to stay in the Senate."

The very next year, in the aftermath of Martin Luther King's most dramatic and politically successful campaign in Selma. Ala., Congress passed the Voting Rights Act. That law forever altered the course of Southern politics and the role of blacks in it. Thurmond was only one of many who read those returns correctly and retreated from the extreme racial positions of the recent past. He, like the nation, moved into the mainstream of the center.

Last week's vote, by Thurmond and for the citizens of Washington, D.C., had a dual historic aspect. In a special sense Washington residents have been without the full guarantees of American citizenship -- have been, in fact, unjustly taxed and dictated to and ruled without representation -- because of deep-seated and ancient fears over race.

Because the Constitution grants Congress the exclusive power of legislation for the District of Columbia, the people of Washington have been at the mercy of those who control Congress. For generations that control was vested in the hands of Southerners. It is one of the ironies of history that the Confederacy, which never was able to capture Washington during the Civil War, for years held it as a helpless pawn.

The one-party rule that dominated the South for decade after decade, plus the old, entrenched seniority system, gave Southerners the chairmanships of the congressional committees. They held the power of life and death over the District of Columbia. The way that power was exercised remained one of the blights of the American Democracy.

There was nothing secret about it. One of the last and great battles of the old segregationists was over keeping control of the nation's capital.

"I wanted this position so i could keep Washington a segregated city," explained the notorious racist, Theodore G. Bilbo of Senate District of Columbia Committee. Mississippi, after he became chairman of the, Bilbo was only saying out loud what everyone knew; that Washington, the city, was singled out in the nation by the racists as a fearsome, crime-ridden city with a black majority -- the very reason, in that warped thinking, for Washington's problems. In fact, Washington citizens for many years had been ruled by a mayor-council form of government, and then were governed by a territorial form with an assembly, governor and delegate in Congress. Citizens had the vote. All that was taken away more than a century ago.

The reason was not constitutional, as you bear argued even today. It was political --and it was racial. After the Civil War the black population of the District of Columbia was growing rapidly as former slaves poured in from the[WORDS ILLEGIBLE] the blacks would soon hold the balance of power, if not indeed actually be controlling affairs. They stripped all citizens of their rights to keep some citizens -- the blacks --from having any.

That historical fact was stated precisely and bluntly almost 90 years ago when Sen. John Tyler Morgan of Alabama, a Confederate veteran, told his colleagues why it had been necessary to abolish popular suffrage and local representative government in Washington, D.C.

"Now the historical fact is simply this," Sen. Morgan said, "that the Negroes came into this District . . . and they took possession of a certain part of the political power of this District . . . and there was but one way to get out -- so Congress thought, so this able committee thought -- and that was to deny the right of suffrage entirely to every human being in the District and have every office here controlled by appointment instead of by election. . . The Senate and the House of Representatives in order to preserve property rights and the decency of administration in the central government of the United States here around the very footwalls of the Capitol: found it necessary to disenfranchise every man in the District of Columbia . . . in order to get rid of this load of Negro suffrage that was loaded in upon them. That is the true statement. History cannot be reversed. No man can misunderstand it."

More than a great wrong was righted by the Senate last week. That vote represented a coming of age of Washington, and the dawning of a new era for the nation's capital.

No city has changed more drmatically in the last decade. Anyone returning today after an absence of years can't help but be struck by the vitality, range of interests, virtual explosion of cultural activities, and most important, easing of tensions and new pride in the city. A great capital city is rising by the Potomac, and the best days lie ahead, not behind. A sense of maturity and self-confidence now characterizes what was once a dispirited, doubting, sullen and somewhat stagnant political center.

What the Senators did last week, those from the Deep South and the border states. those leading Republican conservatives who joined Democratic liberals, was to set the stage. The next act is up to the nation and the states who must ratify or reject the amendment. Opposition to and resentment of Washington are, no doubt, strong. But in the end a vote for Washington is more than a vote for a single city. It is a vote for a capital that mirrors, for better or worse, the country it represents.