It was incorrectly reported yesterday that Episcopal Bishop John T. Walker was the first Protestant clergyman to preach at the National Shrine of the Immaculate Conception. While Walker was the first non-Catholic bishop to lead a service there, Dean Francis Sayre of Washington Cathedral preached at the shrine in 1976.

Area leaders of the Episcopal and Roman Catholic churches stood together in the Washington Cathedral yesterday and pledged renewed efforts to wipe out the centuries-old division between their two churches.

Completing a historic pulpit exchange between the local bishops of the two communions, Roman Catholic Archbishop James A. Hickey mounted the Episcopal Cathedral's high pulpit to exhort the congregation to "search courageously, relentlessly, honestly" for a common understanding of God.

A week earlier, Episcopal Bishop John T. Walker, preaching at the Roman Catholic Shrine of the Immaculate Conception, said the two churchmen jointly "commit ourselves to do all in our very limited power to bring our parishes and people ever closer together" both in community social programs and "in prayer and liturgical worship as well."

The pulpit exchange and joint appeal for interchurch cooperation bracketed the Week of Prayer for Christian Unity, an annual observance of Christian churches throughout the world. The special emphasis this year by Walker and Hickey reflected their efforts to breathe new life into the Christian unity movement, which flourished a decade ago but since has largely been overtaken by other concerns in the churches.

While asserting that the search for unity was "the will of God," Hickey warned against sidestepping the "substantive issues that separate us." Among the "unresolved questions," he said are "differences concerning ordination and the eucharist, women in ministry, apostolic succession," the papacy, the role of the Virgin Mary "in the prayer life of the church" and "certain questions in family and sexuality morality."

Both Hickey and Walker referred to the progress an international commission of Anglican and Roman Catholic scholars is making toward resolving such differences. The Episcopal Church is part of the worldwide Anglican communion. A report of the commission's progress is expected shortly.

Despite such progress, however, Catholics are not permitted officially to receive holy communion in Anglican services. Therefore the services yesterday and last Sunday were prayer services instead of eucharistic services usually scheduled at both institutions.

Ice- and snow-blocked streets and cold kept attendance at the cathedral at just over 600, but well over half the congregation stood in line afterward to greet the two bishops. Some brought small children to be blessed by them.

Walker estimated that about a third of those who greeted the bishops identified themselves as Roman Catholics. "But we usually have quite a number of Catholics attending our services," he said.

Catholic and Episcopal leaders alternated yesterday in scripture readings and prayers from the Episcopal Book of Common Prayer. The two bishops--Walker in his white surplice emblazoned with the red, black and white seal of the Cathedral and Hickey in crimson robe and skullcap--stepped to the microphone together to lead the Apostle's Creed, the affirmation of their common faith.

While Hickey's predecessor, Cardinal William W. Baum, has preached at the Washington Cathedral, no Protestant leader had preached at the Shrine before Walker's appearance last week.