NEW YORK, DEC. 27 -- Local civic and government leaders today denounced two racial attacks in the week following the Howard Beach verdict, saying they showed that race relations in the city remained tense.

Mayor Edward I. Koch (D) issued a statement calling such attacks reprehensible. "We must not and we will not tolerate racism in the five boroughs of New York City," he said.

A gang of white youths, some saying "This is our Howard Beach," beat two black men Friday in Brooklyn, police said. On Wednesday, police said, a gang of blacks beat a white man in Harlem, some yelling: "This is for Howard Beach."

The verdict in the highly publicized Howard Beach case came Monday, with three white teen-agers convicted of manslaughter for chasing a black man to his death in the Howard Beach section of Queens a year ago. A fourth youth was acquitted.

Koch said that although interracial crime exists in New York, he believed the city suffered less from racial divisions than other cities.

Critics, however, said the problem was worse than Koch realized.

"We have to come to grips with the painful reality that racism unfortunately is alive and well in our own town," said Norman Siegel, director of the city's chapter of the American Civil Liberties Union.