The sixth assembly of the World Council of Churches has achieved a breakthrough on Christian unity efforts that could lead to closer ties among all branches of Christendom--Protestant, Roman Catholic and Eastern Orthodox.

Delegates from 300 member churches throughout the world meeting in Vancouver endorsed the landmark "Lima Agreement" late Monday, according to wire service reports. The accord was achieved 18 months ago by theologians from widely divergent churches on three key elements of Christianity: baptism, holy communion and ministry.

In a separate action, delegates adopted a statement on human rights, which reaffirms the responsibility of churches to defend human and religious rights. A further statement on the subject, which is expected to cite specific violations, is still to be debated by the assembly, which is scheduled to end today.

Throughout Christian history, countless schisms and divisions have been rooted in disputes over such questions as infant baptism, whether or not Christ is present in the eucharist or whether authority rests in local church members or in bishops or a pope.

In endorsing the Lima Agreement, so called because of city in Peru where the theologians completed work on the document, the council assembly asked its member churches, which include 400 million Protestant and Orthodox Christians, to study it and report back by the end of next year as to whether they can live with the definitions it sets forth.

While the Roman Catholic Church is not a member of the World Council of Churches, it is involved in the Lima Agreement process. Catholic theologians took part in drafting the document, and the Vatican has sent it to national conferences of bishops around the world for evaluation.

The agreement "gives us the potential of resolving theological differences in a way that is unparalleled in Christian history," said the Rev. Paul Crow, a Disciples of Christ delegate and leader in ecumenical efforts. The assembly's endorsement, he said, moves unity talks from the hands of the theologians "into the churches themselves."

Archbishop of Canterbury Robert Runcie, who is leading the Anglican delegation to the assembly, said the interchurch body's endorsement of the Lima Agreement "gives a pointer for the future far wider than mere theological debate." He said it would give a boost to unity talks the Anglican Church is conducting both with Catholics and with non-Catholic churches in Britain.

Monday's action also called for an international conference in 1987 or 1988 to evaluate the progress and determine next steps.

The resolution adopted on human rights noted that "the violations of human rights in many parts of the world have become more widespread and severe." Without citing specific cases, it adds that "churches must confess in humility that they have not done enough to counter forces of evil and death, at times even being in complicity with them."