A national organization of black Catholics has demanded for dismissal of the superintendent of Catholic schools here for taking a leave of absence to serve as director of Catholic affairs in Ronald Reagan's presidential campaign.

In an angry letter to Archbishop James A. Hickey, Robert L. Robinson, coordinator of the National Black Lay Catholic Caucus, criticized the school official, Leonard DeFiore, for "an impardonable conflict of interest" in leaving his school responsibilities for politics at the beginning of the school year. Robinson demanded DeFiore's dismissal.

A second organization of black Catholics, the Secretariart of Black Catholics of the Washington Archdiocese, also expressed sharp disapproval of DeFiore's action. Charging that the educator's identification with a political candidate "jeopardized Dr. DeFiore's effectiveness as superintendent of [Catholic] schools, especially in the black community," the Secretariat asked that the educator's "tenure as superintendent be seriously reviewed." But the Secretariat stopped short of calling for his ouster.

The action of the Secretariat is unusually bold for a Catholic body since it is, in effect, criticism of the archbishop for granting DeFiore's leave of absence.

Neither DeFiore nor Archibishop Hickey could be reached yesterday for comment.

Part of the criticism of DeFiore hinges on a letter he wrote in September on the letterhead of the Catholic school system, announcing his plans to work for Reagan and detailing reasons for it. The letter read in part:

"For the first time in U.S. history a major candidate for the presidency has specifically voiced views on major issued which are so precisely compatible with values and interests of great importance to the Catholic community." President Carter, the letter continued, "has taken the opposite position" on such issued as tuition tax credits and abortion.

The letter went not only to all priests and school administrators of the local archdiocese, but to Roman Catholic bishops and school superintendents throughout the country.

There are 109 elementary and high school in the archdioces, with an enrollment of more than 47,000 students.

Robinson and other critics of DeFiore charged that this action constituted a conflict of interest and what Robinson termed "a breech of public trust." Robinson added that "Catholic parents in Washington . . . do not pay tuition or make collection donations to have their children's teachers hear about the virtues of a political candidate."

The Secretariat for Black Catholics maintained that disclaimers from the archdiocese that DeFiore's endorement of Reagan did not represent church policy "has little or no effect on the perceptions of the general public, especially the black community."

Pat Canan, who is acting superintendent in DeFiore's absence, said yesterday that the school's office had received reactions, "some for, some against," the superintendent's actions. When DeFiore first sent out his letter detailing his plans, "there was some questioning why, as superintendent, he should have done what he did," Canan said.

Daniel F. Curtin, principal of the archdiocesan Mackin High School, said "a number of people" in the archdiocese are upset both over the letter from DeFiore, which Curtin said "got rather political," and by the fact that neither the archdiocese's board of education nor any other representative body had been consulted about granting him the leave. Curtin said DeFiore has a "good record" as an educator, but expressed concern that the matter had not come before any of these groups.