In an unprecedented display of brotherhood, the once white-hating American Muslim Mission rallied several thousand strong at Constitution Hall yesterday at an Interfaith Community assembly, with Protestant, Roman Catholic and Jewish clergy of the area as honored guests.

Imam Khalil Abdel-Alim, local head of the religious community once known as Blask Muslims, called the transformation of his denomination "a miracle" that grew out of devotion to God and deeper study of the Koran and challenged Christians and Jews to live up to the truth of their religions.

"You are looking at a community that used to believe that there was no accepted and recognized by God but black people . . . that people with a white skin . . . were the devil himself," said Abdel-Alim in describing the change of the group since the death of its leader, Elijah Muhammad, six years ago.

"You are listening to a man who used to preach that. . . I risked my life on that belief," he continued. "Anyone who was in the community more than six years ago used to believe that."

On contrast, he said, "You are looking at a man now who can look at Rabbi [Eugene] Lipman" (who had spoken to the crowd earlier in the afternoon) and call him my brother -- not my Jewish brother, but my brother . . . because I see him as a human being."

"Some of you have problems with that. . . . You'd better get to the Koran, get on your knees and ask God for some understanding of the Koran," he said.

Following the death of his father in 1975, Wallace Muhammad, now known as Imam Warith-Deen Muhammad, brought about revolutionary changes in the then black separatist movement which was formerly known as the Nation of Islam. The changes, the younger Muhammad says, were designed to bring it into the mainstream of American life and closer to the religious truths of the Koran.

In addition to abandoning its racial teachings, the American Muslim Mission, as it is now known, had strengthened ties with traditional Islamic movements throughout the world, stressed the need for dialogue and understanding with Christian and Jewish communities and encouraged members to take full and active roles as American citizens.

Abdel-Alim, who serves in national leadership roles of the movement as well as being the spiritual leader of the Washington group, credited the changes brought about by Warith-Deen Muhammad to the latter's prayerful study of the Koran, the same kind of study which he urged on Christians and Jews of their holy books.

Since the founding of the Interfaith Conference here three years ago, Abdel-Alim has been active in the body, which includes representatives of Protestants, Catholics, Jews and Muslims. Many of the speakers at yesterday's rally are also active in the Interfaith Conference.

Yesterday's audience, which was overwhelmingly American Muslim Mission, vigorously applauded Rabbi Lipman, who struck the theme of many of the clergy present. "We will not agree on religious matters," the rabbi of Temple Sinai said, "but God requires of us that we work unceasingly in order that justice is done in our town. I rejoice in the fact that all of us can come together to make life better for people in this town. . . That is what God expects of us in order for the peace to be real peace."

Other speakers, included Canon Lloyd Casson of the Washington Cathedral, the Rev. Gabriel F. Duffy of St. Ambrose Church in Cheverly, representing Roman Catholic Archbishop James A. Hickey, and the Rev. Ernest Gibson of the Council of Churches.

But it was D.C. Del. Walter E. Fauntroy who was clearly the favorite of the crowd. His down-home Baptist-style sermonette paid tribute to the Muslims, particularly their prison ministry, but it was his contrast of the festive day with bitter memories of the past that called forth the "amens."

"There were those in my childhood who said the day would never come when an interfaith assembly would be held in the DAR's Constitution Hall," he said. It was more than 35 years ago that the DAR refused the use of Constitution Hall to Marian Anderson for a concert. The incident was burned into history when Eleanor Roosevelt countered the slight to the black singer by arranging for her to sing at the Lincoln Memorial.

"Today," Fauntroy continued, "I joun with those of the past who dreamed of this day," and to the delight of the crowd, burst into a spirited version of "The Impossible Dream."