With hundreds of yellow banners, chants and occasional clenched-fist salutes, thousands of demonstrators marched down Pennsylvania Avenue yesterday to protest the Bakke reverse discrimination case now before the U.S. Supreme Court.

The largest group of demonstrators were black college students from Washington, New York and other Northeast states. Many said they had been admitted to college because of affirmative action programs that the suit, brought by Allan Bakke who is white, seeks to ban as unconstitutional.

The march also attracted a substantial number of young whites, many from leftist political groups, as well as demonstrators with banners for other causes, ranging from independence for Puerto Rico to black rule in South Africa.

Official police estimates of the crowd, which was orderly though often exuberant, ranged from 5,000 by the D.C. police, to 10,000 by the U.S. Capitol Police, and 15,000 by the U.S. Park Police.

Jimmy Garrett, D.C. coordinator for the demonstration, told the marchers after they circled the Supreme Court building and gathered at the Capitol steps that 50,000 people took part in the demonstration.

"We said no to racism. We said no to sexism. We said no to Carter," declared Garrett, an associate professor of political science at Howard University. "We said no to thoe eight old white men on the Supreme Court."

In his suit Bakke claims he was denied admission to the medical school of the University the school had set aside 16 of the 100 slots in its freshman classes for minorities.

The California Supreme Court ruled in favor of Bakke, striking down special admissions programs.

Tn October the U.S. Supreme Court heard oral arguments on the case, with the Justice Department arguing that race may be considered in university admissions in order to remedy past discrimination.

However, many of the speakers at yesterday's demonstration strongly denounced President Carter.

Frank Shaffer-Corona, a member of the Washington School Board, declared, "Jimmy Carter is the head of the racist (American) government . . . Jimmy Carter's peanut butter money is tainted with the blood of South African workers. We are going to have another racist judge (on the Supreme Court) when Jimmy Carter gets appoint a judge."

Shaffer-Corona spoke as the marchers assembled on the Ellipse just south of the White House. He was introduced to the crowd as "the official ambassador of the Chicano nation."

The speakers also included representatives of Asian-American, women's labor union and handicapped groups, many of whom called for unity in what they said was a commons struggle against the unfairness of the American economic system.

Arthur Kinoy, a New York lawyer long active in defending elftist and civil rights groups, said:

"The Bakke decision (in California) is just the tip of the iceberg. . . . We can now see a major conspiracy on the part of the ruling powers in this country to shift the burden of the economic crisis in this country to the backs of the working people."

Sponsors of the demonstration were the National Committee to Overturn the Bakke Decision, the National Lawyers Guild, the Black American Law Students Association and the Peoples Alliance.

Supporters ranged from the D.C. City Council, Central Labor Council of Greater Washington and the Howard University Medical Student Association to hte Socialist Workers Party, the Workers World Party, the U.S. COmmunist Party and Youth Against War and Fascism.

As the demonstrators moved doen Pennsylvania Avenue, Carrier Fairley, of Newark, N.J., a student at Rutgers University in Newark, explained why she was participating.

"How can there be reverse discrimination," she said, "when minorities aren't free now? That (Bakke) thing is crazy."