In his lifetime, this was a city that wanted to shut out Martin Luther King and his movement for social justice. But now the marquee on Atlanta's Best Western hotel welcomes the estimated 30,000 visitors to a six-day celebration of King's 50th birthday, and on Saturday the post offices were packed when a 15-cent King commemorative stamp was issued.

The city of Atlanta celebrates Jan. 15, King's birthday, as an official holiday. But the state of Georgia does not, although it honors Robert E. Lee and Jefferson Davis. Nonetheless, over the last four days tens of thousands of people convened for the occasion -- including President Jimmy Carter, the prime minister of Sweden, the foreign minister of Norway, U.N. Secretary General Jurt Waldheim, Sen. Edward Kennedy, a dozen congressmen and administration appointees, scores of faces from the civil rights movement of the 1960s and the human rights movement of the 1970s.

President Carter, who as governor did not support a proposed state holiday for King's birthday, yesterday afternoon received the Martin Luther King Jr. Nonviolent Peace Prize -- and said that he now endorses the idea of a national holiday.

Today the city will flash back to the '60s as crowds march downtown to the state capitol. But even before the lines of marchers -- which will include Stevie Wonder and mayors Maynard Jackson of Atlanta, Richard Hatcher of Gary, Ind., and Coleman Young of Detroit -- and before the picket signs appear, Atlanta will have felt the full impact of this birthday celebration.

The participants filled six major Atlanta hotels -- the people festive with the reunion spirit, buttonholing one another for serious conversation. And outside Ebenezer Baptist church yesterday, two groups demonstrated against President Carter: one a group of Iranian students; the other, workers from the Southern Christian Leadership Conference protesting unemployment rates.

The recurrent question of both hotel personnel and taxi drivers was, "Are you here for the King celebration? This is just what the city needs!"

Despite all the turmoil, the King birthday commemoration, now in its 11th year, differs from the other large black gatherings in its spiritual emphasis. The constant reminder of spiritual goals, tempers, outbursts and angry viewpoints.

Most of the meetings, including the presentation to President Carter, were held in Ebenezer Baptist Church, home church of the King family.

"The spiritual source of the church is never far from these peoples' minds," said Barbara Williams, staff director of the Congressional Black Caucus. The mood was catching, as Kennedy and D.C. Del. Walter Fauntroy addressed their audiences in a preacher's oratorical style.

Kennedy was the first show-stopper. On Friday afternoon he came in, quoting Martin King and Frederick Douglass, announcing that a bill for a national holiday on King's birthday would be introduced at today's opening congressional session. Rev. Martin Luther King Sr. whooped like he had never heard it before.

Kennedy had a line in his speech that was repeated to drive home a point. And he found that a speaker cannot do that in a Baptist church and expect to keep the speech to himself. Kennedy started with "Now is the time." As he warmed up in front of 16 microphones and an audience of 700 people, the audience stole his line and began calling it out before he did. The atmosphere became raucus. And "Daddy" King, the dean of this rocking Baptist oratory, was bouncing in his seat. Kennedy, knowing that he had struck home, turned around and shook King's hand in the middle of his speech.

Yesterday the timing was not so perfect. Just as President Carter finished his 40-minute acceptance speech of the King Peace Prize, Andrew Young arrived and bounded onto the stage. The audience shouted as the ambassador embraced Rosalynn Carter, Coretta Scott King and the president. Young went to the microphone and said, "Never in Martin's lifetime could he have imagined a president of the United States would receive an award in his name."

Carter had been warmly received by the 800 people in the church. Over the shouts of the demonstrators outside, his speech had been interrupted 16 times for applause.

"The only way to overcome unequal history, which leaves discrimination when the laws are equal, is to promote and defend and enforce the equal opportunity for all disadvantaged Americans in this land," the president said to sustained applause. "And that, again, is what we will do. But we must, and we ill, do more, much more. It is not enough to have a right to sit at a lunch counter if you can't afford to buy a meal."

In private meetings at the White House, Coretta King has been one of the most consistent critics of the president, and their relationship was especially tense when White House support for the Humphrey-Hawkins bill was almost too late. But yesterday was a day of peacemaking, as King told Carter that, "We have observed your restless and relentless struggle." Like all meetings of the Carters and the Kings, this one ended with an emotional rendition of "We Shall Overcome."

The six-day program, which ends tomorrow with a special United Nations session, was a time of celebration and reflection.

"We have to understand the past. It has lessons," said Curtis Harris, a minister from Hopewell, Va., standing outside one of the livelier sessions, a panel discussion on the Equal Rights Amendment.

"But now too many of our own people have decided to take the high road, the road of complacency. We have come through some dog days which are not over. Violence is now perpetuated through legislation and the courts." His was not the only voice of discord.

At the ERA meeting, former Pennsylvania secretary of state C. Delores Tucker was explaining how "bucks, boycott and the ballot" could lead to passage of the Equal Rights Amendment. By her side Addie Wyatt (of the Amalgamated Meat and Butcher Workers), one of the highest-ranking black women in a union, was explaining how profitable discrimination is. Ellie Smeal, president of the National Organization for Women, nodded in agreement.

The small meeting room was too crowded, steamy from the overworked church radiators. Then all the cameras focused on a white woman who wanted to know why the Georgia organizers of the ERA effort were "as white as in Louisiana," and was that true everywhere? The murmurs rose to a rumble. A black woman historian took the microphone and reminded the group of how white women broke from the abolitionist movement "to work for women's rights and didn't think it politically wise to bring the black issue along."

Then Alexis Herman, the director of the Labor Department's Women's Bureau, assumed a peacemaker's role: "Even though sexism is a collective responsibility and challenge, racism is the No. 1 problem."

And everyone seemed to agree with Diane Fowlkes, a Georgia State University political scientist who looked resigned as she said, "We work together informally, but I agree that white women should come in and work in the black struggle."

Elsewhere, the commemoration took more personal forms.

Abdullah Ibrahim, a South African musician brought to this country by Duke Ellington, read silently someting he had written: "If you have not found something to die for, what have you found to live for." Then he played a mournful song on the flute, followed by an angry piano work dedicated to the memory of those who had died in Soweto.

"In South Africa," Ibrahim said a few minutes after he had performed at the weekend's cultural night, "We used to listen to the fights of Joe Louis on the radio, then we watched the work of Dr. King. In the sense of bringing some light into our lives he was the same as Joe Louis. Every time a black American overcame an obstacle, it was a victory for us."

And on the stage at the Wheat St. Baptist church was a tall, voluptuous young woman, her head and body wrapped in black folds. She screamed, acting out the anguish of a mother losing her child. The actress was Yolanda King, the oldest of Martin King's children.

"The arts must be part of the civil reights movement of the 1980s," said Yolanda King, 23, a graduate student at New York University. "There's so much stagnancy and forcees that's so much stagancy and forces that promote disunity. The arts can be a catalyst for change." She and her brother, Martin, 21, added their own contributions to the weekend.

The third male of the family to be called Martin spent most of the weekend wrapped in a butterscotch leather coat running errands and checking last-minute details. At one point he talked to other college students about "a network for social change."

Soft-spoken and shy, the young King said he enjoyed the public role: "I have a good sense of direction. So. I am confident in using that ability. I think that often the youth groups have been the backbone of the movement, and I want to bring some younger people together here."

In a weekend of constant cameras, the public Coretta King was reflective as others spoke of her husband, visibly rigid as Walter Fauntroy recapped the assassination investigation, and congenial as she table-hopped at a luncheon for the public and her board members.

She blushed at the joke "Daddy" King told twice over the weekend about being "present" at his son's conception. She glowed when the contributions of CBS Records for $50,000 and of Don King for $10,000 were announced. And she listened intently, as if she had never heard the story before, when author Alex Haley recalled his Playboy magazine interview with King.

Only once did the countless evocations of her husband's name crack her composure. She joined Walter Fauntroy and Ben Branch (the minister-musician who was taling to King the moment he was shot) while Branch played saxophone and Fauntroy raised his airy tenor in a slow rendition of "The Impossible Dream." The tears flowed freely.

Standing outside Ebenezer Baptist Church, in the windy 20-degree cold, Ruth White, a nurse's aide, said the "legacy" of King had brought her to Atlanta from New York for these six days -- not the events or celebrities, but simply one man's contribution.

"I want to be part of history, naturally, but I am proud of King because he was the first man to have so many achievements and to have his name revered by those who think blacks have none," said White. "Of course, it was beautiful to have President Carter here with the King family. I only hope he meant what he said, that he wasn't appeasing us because this is our day."