The message that came over the loudspeakers yesterday morning at DuVal High School began with congratulations to the "winning girls basketball team" and ended on one harsh and succinct note.

Anyone caught in the hallways, warned principal Lorenza Y. Robinson, would be suspended. "Now, ladies and gentlemen," she said, "you're going back to being students again."

After a confrontation between black and white students Friday resulted in eight injuries, 27 suspensions and three arrests, school officials weren't taking any chances yesterday. With Prince George's County Police patrolling the grounds, "crisis intervention" guards stationed in hallways and a seven-page absentee list, the school was calm, but blacks and whites eyed one another warily.

"Today, everybody's shaky," said Jim Matthews, a black senior. "You don't know if the guy sitting next to you is gonna jump you."

The flareup surprised many students and teachers at DuVal, a school that has enjoyed relative racial harmony since 1970, when a racial clash resulted in 22 arrests and calls for a grand jury probe by legislators who contended a "reign of terror" prevailed at the school.

Since that time the proportion of blacks among the school's 1,800 students has increased from a quarter to a half. The racial change occurred gradually, through busing that began in 1973 and as more black families moved into the county. Students came to DuVal from towns like Greenbelt, Glenarden, Landover, Seabrook and Palmer Park. While maintaining close friendships mostly along racial lines, blacks and whites intermingled in the cafeteria and at sports events.

That mood of peaceful coexistence was suddenly shattered last week.

Friday's fracas stemmed from an incident the day before involving an alleged drug sale gone awry. School principal Robinson said that two black youths, who do not attend the school, allegedly took $10 from a white student buyer who reportedly felt he hadn't gotten his money's worth of marijuana.

The white student chased the two youths, knives allegedly were brandished and threats exchanged. By Friday morning, embellished and contradictory versions of the previous day's event had spread and the word was out that there would be trouble at lunchtime.

The fight began in the rear parking lot, with anywhere from 20 to 50 on each side. Sporadic fighting erupted in the hallways. Someone pulled a false fire alarm, emptying the entire student body onto the concrete battlefield. Passions were further aroused when a white student donned a Ku Klux Klan hood and jumped atop a car, shouting and waving his arms.

"It was outrageous, just unbelievable," 12th grader Cindy Peterson said yesterday. "Everybody was just going crazy."

"Everybody got their 'boys' out there. People were fighting and didn't even know what they were fighting for," David Hockey, a junior, recalled.

With help from county police and additional school security personnel, called in earlier by wary administrators, the melee was quelled. Students returned to classrooms, where they were ordered to remain until they were dismissed room by room.

The racial flare-up came as a shock to Dr. Dale Woodburn, who retired as the school's principal last summer after a decade. "It was a little tense" when he took the job in the wake of the 1970 trouble, he recalled. Blacks and whites wanted separate bands for the senior prom, a Black Awareness Club formed and large numbers signed up for an elective course in black studies.

By 1980, he said, "there was a good deal more acceptance in the way students got along, treated each other."

Lorenza Robinson, the school's first black and first female principal, said she hadn't noticed any racial tension during her first year at DuVal. "These kids are very easy to deal with," she said. "I was shocked, I was amazed and I was ashamed ot it. I thought my kids might turn on outsiders but not on each other."

Over the weekend, she said, administrators phoned parents of 15 students "we identified as directly involved." The students were ordered to remain home yesterday while school officials sought to determine their role and what, if any punishment, was appropriate. The only expulsion being considered, she said, involves the student who wore the KKK hood.

She said strict security would remain in effect for a while. Yesterday, guards carrying walkie-talkies were augmented by teachers who spent their free periods patrolling the building and 22 administrators dispatched from the school board's central office.

Some students yesterday predicted more trouble once the guards leave. But Robinson sought to forestall any reoccurrence, calling a faculity meeting and sending a written message home with each student. The message described the events of the last several days and called for volunteers for a "parent rumor control plan, if needed."

"Many of the problems might have been avoided if students looking for trouble had not had an audience," the message said.

Before dismissing the students yesterday, the principal took to the loudspeaker once more. She was proud, she said, of the way they had conducted themselves this "very nice day" and added, "Hopefully, we'll have more days like this in the future."