The Supreme Court yesterday stopped an effort by low-income blacks in Westchester County, N.Y., to invalidate federal sewer-construction and wilderness-preservation grants to a high-income community that is 98.7 per cent white.

The court let stand a 6-to-4 decision by the Second U.S. Circuit Court of Appeals that the blacks did not have the legal right to sue because the grants caused them no injury.

The blacks live outside the Town of New Castle, a New York City suburb in Westchester County that received $400,000 from the Interior and Housing and Urban Development departments.

In a suit intended force predominantly white communities to broaden fair-housing opportunities, the blacks argued that the grants violated the affirmative duty of the government - acknowledged in the civil rights acts of 1964 and 1968 - to eliminate housing discrimination.

The grants reinforced the existing pattern of New Castle's primarily single-family, white housing, the blacks said.

Rejecting their claim, the appeals court majority cited a 1975 ruling in which the high court - on constitutional grounds - rejected a challenge by nonresidents of Rochester, N.Y., to zoning laws that excluded low-income dwellers.

The minority said, however, that the 1975 ruling was no bar to a complaint based on noncompliance by federal agencies with the mandate of the civil rights laws.

The blacks had been injured and therefore had standing to sue because the grants had the effect of perpetuating their "ghetto living conditions," the minority said.

In other section: SCHOOL DESEGREGATION

The court granted a petition by the Dayton, Ohio, Board of Education for review of a desegregation plan that the board claims to be overkill. The plan, upheld by the Sixth U.S. Circuit Court of Appeals in May, would require regular and permanent busing of about 15,000 students and would require each of 66 schools in the system to have a black enrollment of between 33 and 63 per cent. The total school population is 48 per cent black. FALSE IMPRISONMENT

In 1974 the New York Court of Claims ruled that Alphonso Vitello had been falsely imprisoned in state mental hospitals for 26 years - from the expiration of a robbery sentence in 1940 to his voluntary commitment in 1966.

Taking into account improper procedures that had resulted in the imprisonment and the "degradation, indignities, humiliation and frustration" he had suffered, the court awarded him $100,000.

In making the award, the court noted that the same records had led a psychiatrists for Vitello to testify that there was no evidence Vitello ever had been psychotic, while a state psychiatrist testified he was psychotic even in 1966.

The New York Court of Appeals nullified the award, agreeing with the state that Vitello at no time during the 26-year period had proved he was sane. Yesterday the Supreme Court said it lacked jurisdiction in the case and dismissed Vitello's appeal. DAMAGE AWARD

In 1972 a white policeman in Denver, claiming self-defense, fatally shot a 15-year-old black in the back of the head. Under a law strictly limiting liability in such cases, a jury awarded the victim's mother $1,500. The high court agreed yesterday to review her claim that she was entitled to sue the policeman and the city and county of Denver under an 1871 federal civil rights law that does not limit financial liability. REAPPORTIONMENT

Mississippi is 37 per cent black. But only four of Mississippi's 122 state representatives are black, and none of Mississippi's 52 state senator is black.

Yesterday, for the fifth time, the high court entered an 11-year-old reapportionment battle. It agreed to review a new apportionment plan devised by a three-judge panel that would leave the situation mostly intact until 1979.

The Justice Department says the plan improperly dilutes black voting strength. Mississippi officials say it disrupts the integrity of the state's political system. PRISONERS' MAIL

The court agreed to review a decision by the Ninth U.S. Circuit Court of Appeals that a prisoner's right of free speech is violated when his jailers, without wrongful intent, neglect to mail his letters. AIR CRASH

While still over Atlanta's De Kalb-Peachtree Airport moments after takeoff in February, 1973, a Lear jet ingested a large number of birds into its two engines, lost power and crashed. All seven persons aboard were killed.

For several years before the accident De Kalb County's garbage dump at the edge of the airport had been attracting thousands of birds while federal and county authorities discussed the possibility of closing it.

Last August the Fifth U.S. Circuit Court of Appeals blocked suits by the victims' relatives and an insurer with a ruling that federal common law immunizes the county from suits. Yesterday the high court agreed to review the ruling.