Thirty-six black students from Boston have quit the high school they were bused to in this suburb, claiming that white students have threatened them. Some of the whites boasted Ku Klux Klan connections in their yearbook biographies.

"These kids are afraid to go to the bathroom alone," said Jean McGuire, executive director of the organization that operates the busing.

The black students were bused 19 miles every school day under the area's voluntary school busing program, which was designed to promote intergrated education, authorities said yesterday. Several other local blacks will remain in the school this fall.

Those from Boston who chose to quit are the first to withdraw en masse from a suburban school in the 12 years if the program.

"The climate's not conducive to learning if you've got to look behind you all the time," said Carolyn Jackman, a liaison officer for the Metropolitan Council for Educational Opportunity, which operates the busing and is known as Metco.

Under the program, nearly 3,000 Boston minority students are bused to mostly white schools in the suburbs.

The students and their parents voted last week to quit after a fight between whites and blacks at the Concord - Carlisle Regional High School the final day of classes June 28. Black students claimed the fight was promoted by racial threats from white students.

A carload of whites allegedly trailed the blacks' bus after the fight, threatening, "Okay, you niggers, we'll get you next September," said Betty Roylston, a Boston teacher whose son, Brian goes to school here. She said Brian, a 15-year-old freshman, was knocked down in the fight. She voted to withdraw the children.