Evangelical Protestant parents who began adoption procedures in 1975 involving 20 Cambodian orphans have finally received legal custody of the children.

Judge Lester Olson of Superior Court has accepted the recommendation of the Los Angeles County Department of Adoption that the children be allowed to stay with the Christian parents. Adoption papers have been completed.

The children were brought to the U.S. by World Vision International in the 1975 "babylift" operation after Cambodia fell to the Communists. Placement of the children was handled by Family Ministries, a Whittier-based private Christian adoption agency that placed the children only with members of evangelical Protestant churches.

Dr. and Mrs. Richard Scott, a couple who wished to adopt a child and did not consider themselves evangelical Protestants, filed a suit challenging the religious requirement of Family Ministries. Judge Olson ruled in October, 1975, that the religious stipulation was illegal.

The judge allowed the children to remain with the Christian families in which they had been placed by Family Ministries. But he transferred custody of the children from Family Ministries to the Los Angeles County Department of Adoption. He said adoption proceedings were invalid until litigation was completed.

The county reportedly found that the children were happy in their prospective adoptive homes. Its officials decided that because of the length of time required in litigation, delaying the adoption decision was not in the best interest of the children. The children are now 2 1/2 to 9 years old.