Karen Cheu writes for the student newspaper, runs on the track team and is among the top students at her predominantly white high school in suburban Fairfax County. But in her honors government course, where she is one of two black students, she rarely speaks up.

"If I say something wrong, I think people are going to say: 'Typical black child,' " said the South Lakes High School senior. "When you're wrong and you have 29 white people sitting in there, you're really wrong."

Alicia Pessagno felt similarly uncomfortable as a white student four years ago when she entered the predominantly black Suitland High School in Prince George's County. She clung to the walls in the crowded corridors and apologized nervously if someone brushed against her, she recalled recently.

She is now more at ease. But she still acknowledges, "It's hard to be a white person here."

Cheu and Pessagno do not know each other. Their schools are more than 25 miles apart, in strikingly different communities, with student bodies at opposite ends of the socioeconomic spectrum. But the two teen-age girls share a singular experience: They know what it means to be the other race in a overwhelmingly one-race school. It is not always a comfortable feeling.

The issue of race has surfaced in recent weeks at both schools, emerging under the painful glare of publicity amid charges that, even in the most egalitarian institutions, traces of discrimination remain.

At South Lakes, a high school for the mixed but mainly middle-class planned community of Reston, three dozen black parents signed a petition alleging racial discrimination against their children. That petition prompted an official investigation, a day of sometimes angry meetings by black students, anguish and resentment among school staff, and troubling questions for many Reston residents.

At Suitland, a high school drawing principally from blue-collar neighborhoods, a group of white parents pulled their children out of school temporarily after a series of fights and disturbances that some claimed were racially motivated.

Parents, teachers and students at both schools say that racial violence is extremely rare, that racial tension is infrequent and that epithets common in years past are seldom heard.

Some students eagerly volunteer that they socialize in integrated groups. To them, the word "racism" means segregated schools and separate water fountains -- images of the past for a generation that grew up after the peak of the civil rights movement.

Their schools are like those anywhere else in one important aspect, they say: Students who jump into studies and extracurricular activities earn success and acceptance.

But other students at the schools say that being a minority is a handicap. And there are subtle signs of a self-imposed segregation that parcels the lunchroom crowd into clusters of white and clusters of black.

Some middle-class white students at South Lakes speak contemptuously of blacks from Reston's lower-income housing projects who "pound on the walls" or "bring their babies to school." The more sophisticated among them, however, say those statements stem from divisions of socioeconomic class, not color.

"Middle-class black people get on with middle-class anybody," said one 17-year-old white junior.

White students at South Lakes are quick to point to evidence of racial equality: The school president and several class officers are black, and interracial dating is common. Although students who are better off financially dominate the school, even a lower-class child can climb the social ladder through achievement, several white students said.

But many black students still have a sense of racial isolation in the classroom. One way to ease that, they said, is to gather with other blacks at lunch or in their free time. Kim Costner, 17, likes her white teachers and has white friends, but at lunch often sits at a table of black students, both rich and poor. "Most people go to home base at lunch, anybody they have a common bond with . . . their own kind," she explained.

When the girls' track team heads for a meet, "it seems the blacks get on one bus and the whites get on another," said Rene Yokely, 15, a black sophomore. "We listen to different music and they don't like it. They listen to different music and we don't like it."

Several black students said old stereotypes have not died for many of their peers and some of their teachers. "When your SAT scores are higher than theirs, [white students] are really surprised," Costner said. Some black students, counseled by their parents in prejudice's enduring realities, say they do not worry about what their peers and teachers expect of them. But Cheu said she knows it has an effect: "When someone underestimates you, you underestimate yourself."

Raising teacher expectations of black students underlies the school system's attempt to lift lagging academic achievement by minority students. Among the disturbing statistics: At South Lakes, only 5.9 percent of those in the gifted and talented classes are black, even though blacks make up 14 percent of the 2,200-pupil school.

That disparity was one concern that led black parents to file their petition, which split the school and shocked many whites in Reston, founded two decades ago to be a community without barriers of income or race. Previously, signs of prejudice had been confined to the occasional racist grafitto or infrequent black-white fights that trouble most suburban schools.

But some blacks were not surprised. "When you think you can put your child in a pristine setting like Reston and believe you won't have problems, you're naive," said black parent Donald Grant. "Reston is like every place else, but it's a little richer than every place else."

Amid the self-questioning that followed release of the parents' petition in February, Costner and Cheu, who have thrived as blacks at South Lakes, organized an all-day meeting of black students. They were stunned to hear complaints, especially from poor blacks who said that they were eagerly recruited for basketball, but not encouraged to do as well in class. "My eyes were opened," Cheu said. "A counselor reaches out to me, but what about the kids who really need it?"

And even the blacks who do well say they are not exempt from subtle racism in the classroom -- a teacher calling on a black student to provide a translation for "watermelon" in Spanish class, for example.

Middle-class white students say lower-class white students get no more academic encouragement than poor blacks. In both cases, they say, it is personal motivation and parental pressure, not help from the school, that produces academic achievement.

Black complaints are not unanimous, and many black students talked of their teachers with warmth and respect. One ninth grade girl spoke with pride of a white teacher who organized -- on her own time -- an after-school workshop on "thinking skills" for minorities. Said Leon Dockery, 18, senior class vice president: "Everybody has the opportunity to be treated equal."

But Dockery is bothered by one allegation in the parents' petition: Blacks are suspended in disproportionate numbers. Black students said groups of black youths in the hallways are automatically viewed as suspect and told to move on, but white groups are not. The school system investigation of the parents' petition concluded the suspensions were all justified.

The lunch bell rings at Suitland High and, in an instant, the hallways are choked with a moving mass of bodies. In the corridors, how and where one walks is a measure of status.

White students -- who make up just over a tenth of the 2,169 students -- often "hang along the wall and hope to vanish," teacher Karol Thompson said. Two decades ago, when black students were outnumbered, Thompson said, they were more likely to be shy and intimidated. "It isn't any fun to be a minority if you're a kid," she added.

Thompson has taught at Suitland for more than 20 years, watching the school and community change from predominantly white to predominantly black. The school and its problems, she believes, are merely a reflection of the community, a working-class neighborhood of garden apartments and aging houses near the District line.

Thompson was there during the racial brawls and turmoil of court-ordered busing in the 1970s and other, nonracial violence, including the shooting death of a student in 1976.

But despite the problems, Thompson said, "some real positive things are happening . . . . There are black and white friendships . . . . It just takes a long time."

The suggestion of racial strife was resurrected at Suitland after a fight involving two groups of students on March 7. Although the clash began between two white boys, it was followed by a series of smaller fights and disturbances, some of which were racial. The white parents who kept their children home demanded that administrators take steps to calm the school.

During a period of collective introspection prompted by the incidents, many white students have dismissed the charges of racial tension, saying they are happy and accepted at Suitland. Others confess they feel left out, even afraid.

Both black and white youngsters agree that they tend to group themselves by race, at lunch time, in classrooms, and after school. This phenomenon, they argue, is not racist, but typical of society at large.

"It's just natural," said Veda Gross, a black 16-year-old. "Racism is obsolete to me."

Business teacher Alberta D. Hamilton said that while racism is not blatant, "It's here, it's alive and well . . . . It isn't a lot different now than 30 years ago when I was in Alabama. Whites feel they're basically superior to blacks."

Hamilton, who is black and has taught at the school for a dozen years, said she believes that most of the coveted positions, like pompon girls, are held by black students because whites aren't interested. "If the white students can't be in charge, they don't want to participate."

Her colleague, black counselor Lena Dowden, sees it differently. "I don't think there is a racial rift here . . . . A couple of white kids said there is fear. I think they are in the minority."

Some students at Suitland blame parents for instilling racial bias in their children. "Black parents who grew up [with] discrimination . . . grew up to hate white people," said Trenna Nelson, a black sophomore. "And they teach their children that."

"That's silly," said Gross, the black 16-year-old. "That was the '60s, this is the '80s."

Nevertheless, some white students say they feel isolated. Freshman Sherri Hendrix, who said she is the only white student in most of her courses, told of a class discussion on slavery in which the other students turned to look at her because she was white. "I was embarrassed."

She said she ran for freshman class president, but, "there was no way I could win, because I was white." And she has concluded that the way to get by is "keep your mouth shut and don't look at anybody."

But there is also a feeling among students, white and black, that claims of harassment or exclusion may be simply a convenient excuse.

"It's the responsible ones that get along the most," said sophomore Debbie Carlson. "I'm white and I'm sitting here with my black friends."

Senior Pessagno said she has established herself and her confidence at Suitland by joining clubs, playing sports and earning good grades. "You have to say, 'I am who I am, accept me.' "