Continuing a six-year trend, black students in Montgomery County were suspended from junior and senior high schools at nearly three times the rate of white students, although overall suspensions for both races declined slightly this year compared to last, according to a new report.

The report, released yesterday by the county school system, contains a six-year breakdown of student suspensions by race in each of the county's 43 junior and senior high schools.

Black community leaders criticized the school administration yesterday for failing to deal with a "serious suspension problem" facing black students.

"I'm extremely disappointed," said James L. Robinson, chairman of a citizens committee that monitors minority relations in schools. "We were promised that some significant changes were going to take place this year, but frankly, not a lot has happened."

School officials could not account for the continuing disparity in suspension rates, but said that the slight decline in suspensions was a positive sign.

"I think we still have a serious problem in Montgomery County, but the numbers and percentages of black students suspended have decreased," said School Superintendent Wilmer S. Cody.

Two years ago, the school board ordered the superintendent to develop a special program to increase minority performance in the classroom and minority participation in higher-level academic courses and extracurricular activities.

Citing that program yesterday, Cody said: "We need to continue on with the priorities related to achievement and participation. Success in that area will have some direct effect on suspensions."

Overall, 6.5 percent or 3,125 of the 47,925 students in grades seven through 12 were suspended during the 1984-85 school year compared to a 7.6 percent suspension rate last year.

Blacks were suspended in greater percentages than any other racial group, although the rate declined from 16.3 percent last year to 14.2 percent this year. The rate for whites was 5.4 percent this year compared to 6.6 percent last year.

Hispanic students were suspended at a rate of 7.3 percent this year compared to 7.7 percent a year ago, and Asian students were suspended at a rate of 2.5 percent, up slightly from 2.2 percent last year.

Blacks made up 30 percent of the 3,125 students who were suspended from school this year, although they make up 14 percent of the school population.

A study released by the Reagan administration last year found that minority students nationwide were subjected to a significantly disproportionate share of punishment in public schools.

Such findings often have been cited by civil rights groups as evidence of discrimination, and yesterday leaders of the county chapter of the NAACP raised those concerns here.

"There is something institutionally wrong in the system when we still continue to have that kind of racial disparity," said local NAACP President Roscoe Nix. "You're not dealing in great social and economic disparities here."

Under the school system's suspension policy, students are automatically suspended, usually for one to five days, for fighting, intimidating or insulting teachers, extorting money, carrying weapons, destroying school property and using drugs or alcohol.

Cody said previous studies have shown that most suspensions are warranted, but he added that conditions may exist that cause certain students to act out their frustrations more than others.

"I just don't believe there is that much difference in black student behavior," said Robinson. "There are some very serious things at work here, and my feeling is either they don't know how or they are unwilling to come to grips with them."