As a standing-room-only crowd of more than 600 listened a parade of Montgomery County parents and civic leaders -- most of them black -- told the county school board last night of their strong support for countinuing a mandatory black studies course for all school empolyes.

Speaker after speaker called the course, which the board's new majority has proposed making optional, a continuing commitment to the county's black children.

By early today, as the hearing before the board drew to a close only four speakers had supported the action the majority proposes, while 42 urged retaining the course in its present, mandatory form.

One speaker called the hearing a forum for expressing "the power of the county's black constituency" and was loudly applauded.

On Dec. 18, the board tentatively approved, on a 4-to-3 vote, rescinding the mandatory aspect of the 45-hour course. A second vote will be necessary before the action becomes effective.

Last month's meeting was marked by heated protests from black parents that they were denied the opportunity to discuss the issue with the board and shouts of "injustice" and "racism."

The dozens of speakers who gathered last night to protest the board's plans included leaders of a variety of black county organizations, among them the NAACP, the Black Coalition and the National Council of Zegro Women.

"We are ready for you because we have met racial bigots many times before," said Frank Morris of the county NAACP chapter. Addressing himself to the board majority of Marian Greenblatt, Joseph Barse, Carol Wallace and Eleanor Zappone, Morris declared: "You do not understand that true fiscal conservatives are not racial bigots. We will be teaching you this in other lessons in the future and we are looking forward to the experience." Greenblatt, now the board's president, and Wallace and Zappone were elected last November campaigning, in part, for fiscal conservatism.

The black culture course was made mandatory for the system's 12,000 employes in 1975 when the school board determined that greater understanding was needed between staff and black students. The board's new majority claimes that the course is "demeaning" and lowers the morale of teachers and staff.

Hank Heller, head of the County Education Association, bargaining agent for Montgomery teachers, reaffirmed last night the union's support for the mandatory course, but said "it's simply unfair that teachers have to take the course after achool while other employes can get release time to enroll in it."

About one-third of the approximately 40 speakers who supported the course last night were white. One of them, Julia Morrisn, spokesman for the 801-member Montgomery County League of Women Voters, said the organization "fervently supports" the mandatory aspects of the course.

"The league believes this course is an important part of increasing and maintaining communication in our society," she said.

Norman Gelman, representing the Jewish Community Council, accused the board majority of "needlessly exacerbating racial tension... If you consider this simply a pro forma hearing, you run the risk of further alienating a significant minority in this county," he said, referring to the county's 1/ percent black population. Gelman said his organization, representing 200 Jewish civic groups in the Washington area, supports the mandatory aspect of the course.

Approximately 9 percent of school enrollment is black. An equal percent-age of the system's employes is black. Among the speakers expressing opposition to the mandatory aspect of the course was Sylvia Wubning of the Allied Civic Group, which represents about 50 civic associations in eastern Mongtomery County, who said the black culture course "has no direct bearing on classroom achievement."

Michael Goodman, speaking for the 100-member Montgomery Citizens for Education, said, "racial prejudice is one of the worst problems facing this community, but this course should be made voluntary until its worth has been fully assessed."

The vast majority of speakers denounced the plan to make the course optional.

"We don't expect you to solve all the ills of society," said Ruby A. Rubens. "But we do expect you to solve the many racial ills in Montgomery County schools." She got thunderous applause.