The Roman Catholic Church, in a historic theological shift, has opened the way toward recognizing the validity of the Anglican priesthood by the turn of the century, a giant step toward healing the 450-year-old breach between two major centers of Christendom.

A letter from Cardinal Johannes Willebrands, written last July but made public yesterday in London, linked the lifting of Pope Leo XIII's 1896 bull, decreeing Anglican ordinations "null and void," to Anglican acceptance of theological statements developed by an international Anglican-Catholic unity commission. Willebrands heads the Vatican Secretariat for Promotion of Christian Unity.

Several of the 27 Anglican provinces around the world, including the Episcopal Church in the United States, already have endorsed the theological document.

According to Episcopal Bishop Arthur Vogel of West Missouri, who has served on the unity commission since 1970, the move by the Vatican marks "the first time from the Roman Catholic point of view that continuing ecumenical discussion is really leading to the possibility of a change of judgment."

The move is particularly important to Anglicans who have long chafed under the official Roman view that their ordinations were flawed. Episcopalians were especially irked five years ago when Rome agreed to admit Episcopal priests disenchanted with their church's decision to ordain women but required that they be reordained into the Roman church.

Leo XIII's condemnation grew out of the contention that Anglican priests did not share the Catholic view of the eucharist, namely that Christ is actually present in the consecrated bread and wine.

When the Anglican-Roman Catholic theological dialogue commission began its work in 1970, the group focused its attention on three key points: their respective understandings of the eucharist, the priesthood and authority in the church.

"Instead of going back to refight the historical battles" that led to the divisions, Vogel said, the commission sought instead to describe contemporary practice and belief in relation to the three areas.

"We discovered we were essentially living the same life in the two communions," Vogel said.

The commission completed its work in 1982. Anglican provinces have been asked to study the report and decide "whether or not the statement describes the life of the Anglican communion," Vogel said.

The Rev. John F. Hotchkin, director of the ecumenical affairs office of the National Conference of Catholic Bishops, said yesterday that the responses from both churches have been overwhelmingly positive. "It looks like they're saying, 'Yes, you're on the right track.' "

One practical effect of Rome's recognition of Anglican orders would be that members could receive communion in each other's churches. Conceivably, it also could help ease the increasingly grave shortage of Roman Catholic priests.

Rome is not expected to take formal steps to rescind Leo XIII's bull until after the worldwide Lambeth Conference of Anglicanism has voted on the theological statements in 1988.

By that time, unity moves may be stalled on another thorny issue: ordination of women priests and possibly women bishops in some branches of Anglicanism, including the United States and Canada.

At the London press conference where the Willebrands letter was released, Anglican Bishop Mark Santer, cochairman of the joint commission, called that issue "a fresh and grave obstacle to reconciliation" because the Vatican has vetoed ordination of women.