William Miller Sr. and his family fell into step with the orderly throng at the 1963 March on Washington because the equality they had hoped for since the 1954 Supreme Court decision outlawing "separate but equal" schools had been too slow in coming.

"Washington was still a segregated city," says Miller.

Today Miller, 65, and his wife Vinie, 61, are marching again, and they will be joined by their five children, who will bring their own youngsters this time. Twenty years have seen members of the family achieve successes that once would have been unthinkable for a black in America, but their reason for marching is much the same as it was in 1963. Things are better, but not good enough.

"The improvement hasn't gone as far as the laws said it should go," says Miller. "Blacks haven't made it into the mainstream yet."

Five generations of Millers currently live in Washington and its suburbs. They range from toddlers to Rena Nix Miller, 95, who provides the family's views on race relations with the extraordinary perspective of one born to a family of former slaves in South Carolina.

A frail, gray-haired woman who still has a strong voice and a keen mind, Rena Nix Miller has been witness to much more than a lifetime of change since she was born the oldest of 13 children in the small town of Hodges in 1888.

"Whites. . . they had all the good parts," she says. "We had nothing at all." Black children went to school only four months of the year, she recalls, and were expected to work in the fields the rest of the time. When school buses came into being "white children rode the bus. . . the colored rode the road. They blacks have made progress. Well, they're just getting along better in every way. Now they have a lot of rights."

Certainly her grandson Michael, a 31-year-old Yale University and business school graduate who earns $38,000 a year as finance director for an organization that raises money for rural Africans, proves her point. Yet despite their vastly different experiences, grandmother and grandson agree that some things have not changed.

"Regardless of any success I've achieved thus far, I was born a second class citizen," says Michael Miller.

Along with four brothers and sisters, Michael Miller grew up in a modest family home on 34th Place in the River Terrace subdivision in Northeast. Most of them have gone on to middle-class incomes and satisfying careers that are far removed from the bitter hardships of past generations.

Their parents were both born in the South and came to Washington during the Depression. Except for a tour of duty in World War II, Miller crisscrossed the country on trains for 39 years as a sleeping-car porter, a life "on the rails" that was one of the more enviable jobs a black could hold then. Miller became a shop steward and eventually the last president of the Washington local of the Brotherhood of Sleeping Car Porters.

Vinie Queen Miller, who became his wife in 1947, came here with her father in 1941. Her first job here was doing domestic work in Silver Spring, but she later worked for the federal government, first as a clerical employe and finally as a supervisor of medical records for Walter Reed medical center.

In the South and in the Washington of the 40s and 50s, there were constant reminders that blacks were not welcome in a white world. "We were both born in the South and we had always been, as all blacks were, victims of discrimination in some form," Miller says. "We were very conscious of that."

Even the happiest of times could be marred. When Vinie and her future husband went shopping for a wedding dress in downtown Washington in 1947, they hardly received a cordial welcome. "They wouldn't let you try it on and then put it back," recalls Vinie Miller.

"Once you bought it, it was yours," says her husband. "Once you tried it on it was yours, too."

Neither Miller nor his wife describe themselves as having been leaders in the struggle for civil rights, but say they always tried to join in. And for inspiration and leadership, Miller had to look no farther than his own union, and its longtime national president, A. Philip Randolph.

Over the years Randolph became a friend of the family, and pictures of the labor leader and various Miller children hold prominent positions in family photo albums. It was through Randolph, who first conceived of a massive protest in the nation's capital, that the Millers came to participate in the 1963 march.

"We were trying to do everything to better the lot of blacks. The march became part of another phase, to get people together to participate. It was my duty to get the Brotherhood men to participate," says Miller.

The memory of the march is still vivid. "It was electrifying," says Vinie Miller. "You were there in a mass of people, white and black. There was a unity there that you could feel."

A retired couple like the Millers could have found sufficient satisfaction in seeing their children turn out so well, and those children might well have found little fault with the lives they have led. Instead, all see the 20th anniversary of the March on Washington as a necessary rallying point for blacks--to hold onto what they have, and to make further gains.

Two of the Miller sons marched in 1963, but have only vague recollections of the experience. One says he has grown up without ever experiencing any overt form of racism. All think attending the 1983 march is very important.

Jacqueline Miller, 28, an accounts manager for Woodward and Lothrop, stayed home in 1963. "My sister and I weren't taken to things like that. I guess they thought it was rough for the girls," she says, but she will march today.

"I think it's time for people to really show support for equal employment opportunities. . . . The treatment of blacks and whites is still not the same. To support this march is an outward sign that we don't accept the way things are."

William Miller Jr., a 33-year-old field examiner for the National Labor Relations Board, lives in Severn, Md., with his wife and two children. He walked in the 1963 march with his father and says "we are, to a certain extent, byproducts of that march. Education and job opportunities opened up and we took advantage of that."

He will march again, he says, because "the same doors that opened for us have been closing for the past 10 years."

It is the youngest son, Stephen Miller, 29, who has taken the most active role in the 20th anniversary march, working full time to help coordinate logistics, who has been most affected by the conditions each member of his family describes.

A carpenter who has been out of work since he was laid off in December, Stephen Miller has been working as the membership director for the National Federation of Housing Counselors, an advocacy group for low-income renters and home buyers.

"There are more black people in jail than there are in college," he says. "There are still 85 percent of us whose conditions have not improved."

It is a view that no one in his family would dispute.

William Miller Sr. was on the rails much of his life and there was never much money to spare. But he and his wife say they tried to raise their children in the church, to have the right role models and to be concerned about what they will confront as blacks.

"We have to keep on pushing. We can't forget. . . ," began Vinie Miller, allowing her husband of 36 years to finish the sentence:

". . . that we haven't got it made."