A woman priest ordained two weeks ago in the Episcopal Church and a woman Lutheran minister have been barred from a planned unity service in an Alexandria Catholic church by the Roman Catholic bishop of Arlington. The church reacted by canceling the service.

The Rev. Pat Park, assistant priest at Immanuel Episcopal Church-on-the-Hill, and the Rev. Marcia Bendermeier, an ordained Lutheran minister, were among six clergies invited by Blessed Sacrament Catholic Church to participate in services next Sunday marking the annual Week of Prayer for Christian Unity.

Blessed Sacrament has for a number of years celebrated the unity week, an observance planned and sponsored jointly by the Vatican and the World Council of Churches, with an exchange of preachers with nearby Protestant churches.

According to Blessed Sacrament's pastor, the Rev. Anthony Juste, the exchange had the approval of the Roman Catholic bishop of Richmond when all Catholic parishes in the state were under his jurisdiction.

The churches in Northern Virginia were split from the Richmond Diocese and Bishop Thomas J. Welsh was installed as bishop of Arlington nearly 3 1/2 years ago.

Bishop Welsh reportedly has been unaware until this year of Blessed Sacrament's method of Christian Unity Week celebration.

Last Tuesday, the bishop expressed to Father Juste his disapproval of the pulpit exchange but added that since plans were already under way and invitations extended, the parish could proceed. However, he directed that the invitations to the women preachers scheduled to participate be withdrawn.

The parish council of Blessed Sacrament decided instead to cancel the entire observance. "Given our commitment to the equality of women in both the community and the church, we couldn't proceed on that basis," explained James O'Brien, parish council chairman.

Bishop Welsh could not be reached yesterday for comment, and his official spokesman said he knew nothing about the incident.

Bishop Welsh takes a traditional view of churchmanship. In a press conference three years ago, just before he was installed in his present post, he spoke out against ordination of women to the priesthood.

Roman Catholic canon law prohibits women priests.

On the question of whether non-Catholic clergy should be permitted to preach at Catholic masses, the Rev. John Hotchkin, ecumenical affairs secretary for the National Conference of Catholic Bishops said yesterday that canon lawyers were in disagreement.

He said that "many bishops" have given permission for such pulpit exchanges and even taken part in them themselves but that others "are more hesitant about that."