The Supreme Court yesterday nullified a plan to desegregate public schools in Indianapolis by busing about 9,500 black students beyond the city limits into school districts that are nearly all white.

the 6-to-3 ruling ordered the Seventh U.S. Circuit Court of Appeals to reconsider its approval of the desegregation plan in light of two recent high court decisions.

These decisions upheld laws and government actions that are racially discriminatory in their effect but have not been shown to be discriminatory in their purpose.

The appeals court had approved the busing of Indianapolis students into surrounding Marion County after finding "an obvious racial segregative consolidted the governments but not the school districts of the city and the county.

Implicitly, the high court found that the consolidation law, called Uni-Gov. had not been enacted with a racial motive.

Three weeks ago, the court ruled that Arlington, Ill, a white Chicago suburb, had not denied equal protection of the laws when it refused to rezone a tract for minority low-income housing because discrimination had not been proved to be "a motivation factor."

Similarly, the court last June rejected a challenge by blacks to an entrance exam for District of Columbia policemen because the test had not been proved to have a "radical discriminatory purpose."

In the Indianapolis case, the did not hear arguments or write opinions. The dissenters were justices William J. Brennan Jr., Thurgood Marshall and John Paul Stevens. In August, Stevens had delayed the desegregation plan pending disposition of the legal challenges.

In a related action yesterday, the court refused to hear a challenge ot desegregation plan that requires busing of about 23,000 black students from Louisville to predominantly white schools in Jefferson County, Kentucky.

The two school cases differed markedly, partly because the Kentucky Supreme Court two years ago had merged city and county districts into one.

The Indianapolis and other recent rulings indicate that the high court is reluctant to uphold sweeping school desegregation orders.

One signal came in 1975, when the court ruled out inter-district busing in the Detroit area unless at least one of the school districts involved in a desegregation order has engaged in racially discriminatory acts.

Another signal came last year, when the court set aside an order to desegregate public schools in Austin, Tex., by busing up to 25,000 students. A more limited remedy would be appropriate, the court told the Fifth U.S. Circuit Court of Appeals.

The Indianapolis case began in 1968 with a Justice Department suit to achieve desegregated schools within the city. The department has opposed the inter-district busing plan as unnecessary and the cause of "fruitless" delay.

The appeals court "seemed to assume there is something wrong with schools containing a majority of black children," Solicitor General Robert B. Bork said in a brief to the high court.

"We disagree," he continued. "So long as schools' instead of one set of schools for blacks and another for whites, it matters not at all whether one particular school has more blacks than whites."

In New York City, Jack Greenberg, director-counsel of the NAACP Legal Defense Fund, said he hoped the department under its new Attorney General. Griffin B. Bell, will not advocate the policies Bork set forth in the Indianapolis case.

During the litigation of the department suit, U.S. District Court Judge S.Hugh Dillin ruled that a desegregation remedy confined to the city limits would make the schools so heavily black - 42 per cent - that whites would flee and resegregation would recur.

He also found that the primary reason for white dominance in the suburbs was a lack of housing for blacks. He attributed this in large measure to the city housing authority, which, he said, was racially motivated when it erected all 10 of its public housing projects within the city. The projects are 96 per cent black.

Dillin ordered the busing of blacks to eight Marion County school districts that were 97.1 per cent to 99.96 per cent white, so that each suburban elementary school would become no more than 85 per cent white.

A divided Seventh Circuit affirmed the order, agreeing that the confinement of the housing projects to the city and the failure of the Indiana General Assembly to consolidate city and county schools i Uni-Gov denied the equal protection of the laws guaranteed by the Fourteenth Amendment.

The appeals court acknowledged that there had been resistance to the inclusion of the schools in Uni-Gov on the ground that a consolidated district would be too large for citizens to control and would raise taxes. But, the court said, "these considerations, although apparently not racially motivated, cannot justify legislation that has an obvious racial segregative impact."

The appeals court chided the Justice Department for resisting interdistrict busing, saying it demands removal of segregation from the Indianapolis schools "root and branch" while condeming "the only relief which can make its demand a reality."

As Solicitor General Bork saw it, however, the appeals court was holding - erroneously - "that a state is required to take affirmative steps to prevent particular school districts from becoming 'too black,' and that failure to take these steps amounts to racial discrimination."

"The Fourteenth Amendment does not prefer black schools, white schools, or mixed schools," Bork said. He expressed doubts that the housing authority had acted with discriminatory purpose.