The Rev. Jesse Jackson told 3,000 mostly black D.C. high school seniors yesterday-on the 25th anniversary of the U.S. Supreme Court decision that outlawed racial segregation in the nation's schools-that they must use rights gained in the last quarter century to become a political power.

Jackson, executive director of Operation PUSH (People United to Save humanity), told the students that they should begin their effort by having every high school graduate this year walk through graduation with a diploma in one hand and a voter registration certificate in the other. He spoke at the D.C. Armory.

"They say young people today are political apathetic," Jackson told the students, "but you are not politically apathetic. You are politically ignorant . . . You don't know your political district, your wards, your ward leaders . . . You don't know what kind of power you have."

Jackson asked students who will be 18 by next November and who are not registered to vote to stand up and form a line. The line, stretching the width of the Armory floor, led to a voter registration table. About 268 students registered to vote after Jackson spoke, according to the D.C. chief registrar of the D.C. Board of Elections and Ethics.

Jackson spoke to the students on the 25th anniversary of the Supreme Court's 1954 decision in Brown v. Broad of Education which outlawed legally mandated segregation in the nation's public schools. All of the students at yesterday's rally were born after the decision. Although most said they had heard of it, few knew of its meaning or that prior to 1954 their school system had been divided, with whites attending one group of schools and blacks another.

Jackson told the students that, as the generation reaching adulthood at the start of the 26the year after Brown, they have the responsibility to combine hard work with the legal rights they have gained.

"Sitting beside white children in school is not going to give you an education," Jackson said. "The Russians didn't launch Sputnik because their children were sitting next to someone . . . If you sit beside someone who has done their homework it is not going to help you pass a test."

"Our job now," Jackson said, as the student gave their full attention to the booming voice of the former aide to the Rev. Martin Luther King, "is to put superior effort behind the law, because the law will not make you a doctor. The law will not make you a lawyer. The law will not make you a scholar. The law will not register you to vote. The law will not help you build political power . . . The law by itself means nothing unless we take the superior effort to make [the Brown decision] real."

Jackson spoke to the students as several city officials, including Mayor Marion Barry, City Council Chairman Arrington Dixon, and school board President Minnie S. Woodson sat behind him.Jackson told the students that because the District is run by black officials city services for black people should be the best in the nation.

"You have a black mayor, a black City Council, a black school board. You have a black everything except sunshine," Jackson said provoking laughter. "It would be the ultimate laughter. "It would be the ultimate disgrace . . . if the D.C. schools were not number one."

Jackson said later that he is campaigning for your Americans, both black and white, to register to vote because there is a growing amount of antiyouth legislation. He cited such examples as budget cuts and tax-saving decisions by politicans that eliminate summer programs and after-school activities for young people. He said that in 1965 when the voting rights legislation was passed, the Vietnam war was beginning and young people were being asked to fight a war while they had no political power. CAPTION: Picture, The Rev. Jesse Jackson greets his young audience after speech at Armory at which he urged young people to register and vote. By Margaret Thomas-The Washington Post