A coalition of Roman Catholic, Protestant and Orthodox Christian leaders has launched a new organization concerned with the defense of religious rights throughout the world.

The new group, calling itself Freedom of Faith - A Christian Committee for Religious Rights, will model some of its activities on patterns set by such groups as Amnesty International and the National Conference Committee on Soviet Jewry.

In addition, said William Sloan Coffin, one of the organization's three presidents, "we will be limited only by our imagination" in focusing world attention on violations of religious rights or in easing the plight of oppressed groups.

He indicated that the new group, while Christian in make-up and orientation, would not limit itself to problem situations of Christians, but might ultimately raise such questions as the "religious rights of Reform Jews in the Middle East."

In official matters, such as determining the validity of conversion to Judaism, the Israeli government recognizes only the religious practices of Orthodox Judaism. Both Reform and Conservative Jews here and in Europe have sought in vain to change the situation.

The Rev. Dr. Alexander Schmemann, dean of St. Vladimir's Orthodox Seminary and also a president of the new organization, asserted that infringement of religious freedom by governments on both ends of the ideological spectrum constitutes "a major issue of our civilization."

Formation of the organization was announced at a press luncheon at the Harvard Club here. In addition to Schmemann and Coffin, the other co-president is the Rev. Joseph O'Hare, editor of the Jesuit weekly magazine, America.

Other backers of the new group, which will be headquartered here, include Archbishop Joseph Bernardin of Cincinnati, a former president of the National Conference of Catholic Bishops; Dr. Carl F. H. Henry, Arlington, a leading evangelical theologian; the heads of several mainline Protestant denominations and top leaders of Eastern Orthodox Christian communions.