The parents of the first black U.S. ambassador to the United Nations don't take morning walks in their neighborhood anymore.

They say they are afraid of crime.

"People will knock you in the head, no matter who you are," said Daisy Fuller Young, whose son, Andrew J. Young Jr., was appointed to the United Nations in 1977.

"Yes," said Dr. A. J. Young St., a dentist. "We used to enjoy those early morning walks. But, well, I guess things have changed.

When the Youngs moved into their neat, two-story brick home 31 years ago, theirs was one of the most comfortable black neighborhoods here - home to black doctors, black pharmacists, college professors, successful small businessmen.

Community life centered around Dilard University, a prestigious black private school. You could walk around the neighborhood, then. It was, for the Youngs and all their neighbors, a proud neighborhood, whose children grew up both confident and challenged.

Two powerful forces came along in the '60s to change all that - a federal highway the civil rights movement. The new expressway knocked down the old oak trees and demolished the well-kept houses. The civil rights movement loosened the fabric of the community, even as it liberated the members. It gave aspiring black families options they had never had before, even as it dissolved their old community ties.

Something was lost among the gains. This is an aspect of the last decade's black progress rarely discussed in newspaper articles. It lies beyond startistical measures, beyond the sociologist's jargon. It is a collection of perceived losses, of dissolved human relationships, which inevitably accompany great social changes.

Old neighborhood ties were broken as more mobile blacks took advantage of a less-segregated housing market and moved in to predominantly white subdivisions like new Orleans East.

The "elite" black schools - McDonough No. 35, Xavier University Preparatory, St. Augustine High - began to lose their "quality" students to predominantly white schools.

Thriving black Catholic parishes, which traditionally played a major role in black life here, began to lose parishioners to formerly all-white Catholic churches.

Nothing was the same anyone. The black community in this city entered what one black sociologist calls "a state of normless."

"The distance between me and the black masses is almost the same now as the distance between whites and the black masses," said Daniel C. Thompson, sociologist, author, and vice president of academic affairs at Dillard.

"We don't go to the same churches anymore, we don't live in the same neighborhood anymore," we hardly do anything together anymore," he said. "But I don't know how that can be avoided. These are the 'gains' we fought for."

The gains are real: the Jim Crow segregation laws are gone. Young people who grew up under their strictures have gone on to high places. Andrew Young is one. Ernest N. "Dutch" Morial, the city's first black mayor, is another, Down on Canal Street now, you will see black secretaries, clerks and bank officials where once blacks did only the wiping up the sweeping.

Similar stresses of change have been felt in other major black communities - Washington or Atlanta or Harlem. But the changes may be felt more intensely in New Orleans because of its unique past. Bound by Tradition

New Orleans is a tradition-bound city, heavily accented by the old French and Spanish cultures, and largely influenced by the Roman Catholic Church. Blacks have shared in, and have helped to shape, those traditions and cultures as much as whites.

The wrought iron grillwork in the French Quarter was made by the free blacks, those of pure African ancestry, and by "free men of color," locally called Creoles - blacks of French, Spanish and American Indian heritage.

Jazz, this country's only indigenous music, came from the New Orleans black Community. So did the blues. Voodoo was practiced here in "Congo Square," right under the nose of Holy Mother the Church, which frowned on such thins.

Thre is also color - mulatto, octaroon and quadroon - and the sad role it has played and, according to some, continues to play in the black community.

There has always been a "black society" here, going as far back as 1718 when the city was founded. Originally, the black upper crust was largely Creoles - "a hot-blooded, self-assertive class, militant and pround . . . [marked by] a firm and perservering belief that they were in every respect the equals of their Causasian fellow citizens," according to Charles Barthelemy Rousseve, a black historian here.

Ambassador Young's roots are in that culture and society. But his father, 81, said the family never looked upon itself as upper or middle class, per se.

"It wasn't really anthing you could put your hands on," Dr. Young said. "You just knew it was there . . . There were certain groups of Negro people in a certain strata of society . . . The Educated Class

"Whenever you went to an invitational affair, you saw the same people. You got into that class because you are educated. A few might have gotten in because they had exceptionally good jobs - one that paid about $6,000 a year, say about 20 years ago."

Many blacks entertained in their homes in the pre-civil rights days, said Mrs. Young."We couldn't go to a lot of the places of entertainment because of segregation," she said.

Frequently the conversation at the black social gatherings revolved around education, segregation and colored progress." Many blacks belonged to the National Association for the Advancement of Colored People, which in New Orleans was as much a social club as a civil rights organization.

To be black and middle class here in the pre-civil rights usually meant you were a public school teacher, a post office worker, an "insurance man," an undertaker - or a Pullman porter. There were many black "mailmen" and pullman workers with masters degrees.

If you were black and educated and Protestant, like the Youngs, you probably sent you children to the all-black, private Gilbert Academy to prepare for college. If you were black and educated and Catholic, a faith espoused by about 25 percent of the blacks in this city, you might have sent them to the all-black Xavier University Preparatory.

In the 1940s, there was only one public high school for blacks McDonogh No. 35. "But the public high school was so crowded, we decided to send the boys to Gilbert," Mr. Young said. Andy graduated from Gilbert before it closed in 1948, but his brother Walter had two years to go. "So, we sent him to high school in Princeton, N.J.," Mrs. Young said. Walter is now a dentist and businessman in Atlanta. Unity in Segregation

In a peculiar way, segregation forced a social unity in the black community. It was not uncommon, for instance for a black teacher to live next door to a black day laborer. There weren't too many places in the city where either could live.

Nor was it uncommon for whites to live next to blacks. That does not mean neighborhoods were integrated. It was simply a matter of physical proximity, the same kind that existed on the plantations of days past.

In these checker board neighborhoods, both blacks and whites knew what the social boundaries were. The de jure and de facto penalties for crossing those lines were severe. So nobody crossed them - at least not publicly.

The Youngs lived in such a neighborhood, in the central business district, before they moved to their present home. Dr. Young was the only dentist on the block.

"I had whites as patients," he said. "At first, they used to come to me after dark. But as we were in the neighborhood a little longer, some of them got a little braver and started coming around during the day."

A neighborhood might be one block white, one block black, a half-block white, a half-block black. Children of both races played together, but understood that the socializing was not to go beyond the age of puberty. After desegregation, white families left these neighborhoods. Invisible Buffers

"The whites fled," said Louis E. Madere, a white city planning official. "Before civil rights, they didn't have to worry because of the [racial] rules. But the civil rights laws knocked down those rules, and the whites who lived next to blacks didn't have their invisible buffers anymore."

Partially as a result, something happened to New Orleans that has happened to cities all across the nation, Madere said; "For the first time, outside of the housing projects, this city has seen the development of poor, all black residential ghettoes . . . just in the last 10 to 15 years."

Many of the black families who left the inner city moved to handsome homes, brick ranch-style and modern apartment complexes, in New Orleans East. Ironically, the expressway that tore up some of the old neighborhoods also made this new life possible, by increasing communter mobility for affluent black families.

On their way downtown to work, the elevated expressway crosses the historic Claiborne Avenue area, where black musicians like Louis "Satchmo" Armstrong and Jelly Roll Morton began their careers.

Claiborne Avenue was once the major entertainment district for all of the city's blacks. Jazz clubs and "tonks" stayed open till dawn. Restaurants served Creole cruisine and the southern black cooking, which later because widely known as "soul food."

But all of that is gone now, taken away by the expressway. Its concrete pillars now straddle what had been tree-lined boulevard.

Only a few black nightclubs remain on Claiborne, patronized mostly by poorer blacks. However, some blacks believe the Claiborne entertainment district would have died a "natural death," thanks to desegregation. One is George "Tex" Stevens, a newspaperman, radio personality, public relations consultant and man about town.

"The younger, more affluent blacks are going to the integrated bars," Stevens said. "They go to the Hilton, to Georgie Porgie's at the Hyatt Regency, and places like that. They don't mind paying two dollars or three dollars for a drink."

Stevens said the erosion of black-operated entertainment in the city is largely connected to the erosion of the old neighborhoods! "There are a lot of hoods hanging around too many black bars now. You don't want to have to step over three or four with guns and knives just to get a drink." Blacks Are Divided

Here, as in other cities, are deepeing diviisons between upwardly mobile blacks and their less economically fortunate black counterparts. Many middle and upper income blacks who, like the Youngs, remained in the old neighborhoods have put up iron grillwork to protect their homes from burglars. "Those people" is a term increasingly heard. Along with the crosion of community, there has been an erosion of trust.

"More and more, the black middle class in new Orleans is becoming alienated from the black masses," said Thompson, the Dillard sociologist. "We are increasingly becoming divided in terms of class."

Dr. Henry E. Braden, who lives in an imposing house in a subdivision fronting on Lake Pontchartrain, describes the gulf:

"When I started practicing here, I used to make house calls in the [housing] projects . . . Sure, there were poor people living the projects then. But hey were working poor people, good people. Hell, hoss, they were fighting like hell to get out of the projects.

"But I would not go into the housing projects now. No way. Crime. People gambling with food stamps. Can you believe that? Gambling with food stamps. That really hurts. In my day, we would have been ashamed."

The rising class of affluent professional blacks are a minority within a majority. New Orleans used to be about two-thirds white. But, now, city officials estimate that about 51 percent of the nearly 600,000 residents are black.

Most of the blacks are poor. According to a study of the city's economy by James R. Bobo, an economics professor at the University of New Orleans, at least 57 percent of all black unrelated individuals were living below the poverty level in 1970; Thompson believes things have grown even worse.

About 25 percent of the black population can be classified as middle class in terms of jobs, education and income, Thompson said. "There is a black middle class here, a black lower class, and virtually no one in between." Free Creole People

Beyond the differences of income and education is another senitsive difference - distinctions of color, which have often translated into social status. Many community observers, like Thompson, feel that the rising black middle class is an extension, in large proportion, of the historic Creole class, the "free people of color" whose Spanish-French ancestry set them apart from black slaves.

Under the relatively benign colonial rule of the French and Spanish, many Creole families prospered - owning nearly $15 million worth of taxable property in the city by 1830. By then, however, the Anglo-Saxon racial standards were working to reduce Creole economic status.

Rousseve, the historian, said the white American rule "found a culture here which was not quite as racist as the one they had set up elsewhere . . . They decided that all non-whites had to be cut down to size, so to speak."

Some Creoles responded by "passing" for white - "passe blanc." Others isolated themselves from the larger black and white populations. Many joined the black struggle.

The legacy of this was generations of intra-racial conflict, based on color. The conventional wisdom, for many years, was that light-skinned people got the best of everything offered to the black community - that they became the "black firsts" in any racial progress.

Andrew Young is a descendant of that heritage. So are Braden and Rousseve. So is Mayor-elect "Dutch" Morial.

According to sociologist Thompson, these distinctions receded in importance during the '60s when black consciousness and civil rights solidarity made the subject unfashionable. But the question of color has become sensitive again, as more blacks, including a large proportion of Creoles , move into the middle class.

During his election campaign, Morial had to straddle skillfully these different worlds. One of his campaign organizations issued a fervent defense of his "blackness":

"Believe us, Brothers and Sisters, 'Dutch' may look white, but he lives and breathes BLACK!"

Morial, who takes office May 1, is impatient with people "who want to dwell on the color thing."

"I have to run this city for everybody, which means we have to work to reduce this color business to zero," he said. Security in Self

The mayor-elect says his political triumph is not a matter of his color but of his own feelings of self-worth.

"It's a matter of feeling secure in yourself," he said. "If you feel secure in yourself, you don't have to worry about an insignificant thing like color. You move."

Morial is talking about another of those intangibles that existed in the old black neighborhoods, even when they were surrounded by segregation. Parents learned how to protect their children from the bruises, how to provide the best they could afford within the confines of Jim Crow.

Andy Young and his brother, riding the city bus to school, used to swipe the Jim Crow signs that delineated the black of the bus: "Seats Reserved for Colored Patrons Only."

Their mother remembers: "We were fearful that the police would put them in jail for taking those signs. And in those days, black boys in jail, well . . ."

The Young brothers were taught to drive, so they could drive to school and avoid the potential for trouble.

Andrew Young, as a youth growing up in New Orleans, was barred from white restaurants and theaters, like all other blacks. But Young's parents made certain that he and his brother traveled, east and west, where they could enjoy integrated entertainment, like any other American citizen.

Dr. Young put it this way: "Those boys never learned how to be inferior."