A proud and jubilant but slightly uneasy Southern community today marked the 20th anniversary of the beginning here of the black student sit-in movement, which speakers said, awakened America's conscience, inspired more than a decade of human rights campaigns and ended second-class citizenship for blacks -- and whites.

The day-long commemoration of the historic action taken by four black college students at a dime store lunch counter downtown was buoyed by the same hand-clapping, foot-stomping and crowd-swaying gospel music and allegory-rich black preaching that had sent countless civil rights demonstrators out to face fire hoses and police dogs, armed only with a prayer.

It was a day when some Greensboro domestics put on dress clothes to welcome home four courageous men. It was a day for applauding quiet, unspoken deeds of heroism of bygone years. More than one former demonstrator publicly choked back tears recalling those times of struggle.

But for all the joy, spirits were occasionally dampened by the uncertainty surrounding a planned march and rally here Saturday called to protest a nationwide resurgence of the Ku Klux Klan. On Nov. 3, Klansmen and Nazis allegedly killed five anti-Klan demonstrators at a Saturday morning protest near a public housing project in the predominantly black and impoverished southeastern section of this textile, tobacco and college town in central North Carolina.

The national coalition of ministers and civil rights groups behind the march has assured city officials that the four-mile march will be nonviolent. The group has expelled from its ranks members of the Communist Workers Party, which organized the Nov. 3 protest, because party leaders refused to vow publicly that their marchers would not be armed. CWP members plan to march anyway.

Late today, Greensboro Mayor E.S. (Jim) Melvin declared a limited state of emergency, giving him the authority to limit sale of gasoline to vehicles only, declaring illegal any possession of firearms, other than on private premises, and giving the police the authority to set up additional lines of protection. March organizers noted the emergency would allow police to search people and vehicles with less hindrance.

Melvin said 300 National Guardsmen would be on duty to assist the city's 427-riot-equipped police, but that no additional guardsmen would be used unless necessary. Gov. James B. Hunt Jr. has sent 150 state troopers to the city.

"It's not a move to scare or intimidate anybody," Melvin said. "It gives us some powers you normally don't have to take care of an overt situation."

A broader set of emergency powers was in effect Nov. 11, during what turned out to be a nonviolent funeral march for the five people slain Nov. 3. But no such declaration was in effect when the killings took place.

Former U.S. ambassador to the United Nations Andrew Young, speaking to a standing-room only crowd of more than 4,000 on the campus of North Carolina Agricultural and Technical State University, urged his listeners to join the march and model their behavior on the nonviolence of the four men honored today.

"They didn't used their fists. They used the power of their minds," Young said to heavy applause.

Todays proceedings commemorated that cloudy Monday afternoon on Feb. 1, 1960, when four freshmen from A&T -- David Richmond, Joseph McNeil, Franklin McCain and Ezell Blair Jr. sat down at a whites-only lunch counter in the Woolworth's dime-store, ordered coffee and refused to leave when they were not served.

The sit-ins continued and were duplicated quickly across the South. Within months, prodded by economic boycotts that sometimes followed stubborn resistance to the sit-down tactics, Woolworth's and stores in nearly 200 Southern cities foreswore "local custom" and began to serve blacks along with whites.

The four who made history 20 years ago were back for breakfast at Woolworth's this morning, older and different men now. McNeil, 37, is a Fayetteville stockbroker with a receding hairline. Richmond, 37, a bearded community worker in Franklin, N.C., is balding at the top. Blair, 38, now a Muslim, changed his name to Jibreel Khazan. Today he wore a white headwrap and matching Islamic-style robe and ordered a banana and glass of water for breakfast.

McCain, 38, is a mid-level manager at a Charlotte textile firm. He is a heavier man than the stocky 18-year-old A&T freshman from the Deanwood section of northeastern Washington, D.C., (he graduated from Eastern High School) who won a place in civil rights history.

The four spent much of the day today recapping events of two decades ago, recalling their motives, their thoughts and even their youthful mischief at assuring each other that no one would be "chicken" and back away from the long-planned protest.

Theirs was not simply a dispute over a cup of coffee. McNeil said. "Within our hearts and within the framework of this country we had constitutional rights to pursue our pleasure or our work in any way we saw fit," he said. "What we were after was not only the ability to make the choices, but to implement them."

The four and other speakers today frequently underscored a contention that the civil rights struggle had not won economic equality for blacks. But the four men repeatedly backed away from any attempt to portray themselves as new black leaders of the 1980s.

"Who am I?" McCain told persistent reporters at one point. "I'm just Franklin McCain, one of the persons who just happened to participate."

Twenty years ago, Greensboro's city fathers and Woolworth's tried to thwart the sit-ins, but yesterday they applauded the anniversary. Mayor Melvin declared an official weekend of observance. Gov. Hunt declared Feb. 1 "civil rights and equality day in North Carolina."