The Vatican yesterday named Bishop Donald W. Wuerl, whose earlier appointment to take over duties of Seattle Archbishop Raymond Hunthausen triggered nationwide protests, as bishop of Pittsburgh.

Wuerl, 46, a Pittsburgh native, has been without an assignment since last May, when a top-level committee of U.S. bishops persuaded Pope John Paul II to restore Hunthausen's status and replace Wuerl with Coadjutor Archbishop Thomas J. Murphy.

The Vatican maintained that Hunthausen, a peace activist and liberal churchman, was lax in enforcing church doctrine in five key areas: marriage annulments, liturgy, ministry to homosexuals, moral issues in health care institutions and the discipline of his priests.

In a move unprecedented in the U.S. church, he was stripped of his authority in these areas and the responsbility was handed to Wuerl, an arrangement that everyone involved, including Wuerl, eventually found unworkable.

Wuerl's appointment to the Pittsburgh post came a day after his predecessor, Bishop Anthony J. Bevilacqua, 64, was installed as archbishop of Philadelphia, succeeding Cardinal John Krol, 77.

As a protege of Pittsburgh's late Cardinal John Wright, Wuerl has long been viewed as on the fast track to ecclesiastical advancement. In 1978, he held special permission, as aide to Wright, who used a wheelchair, to attend the conclave that elected Pope John Paul I. He was the only noncardinal present.

He has been a frequent guest in the Krakow residence of the man who is now Pope John Paul II.

Before his Seattle assignment, Wuerl, who is a graduate of Catholic University and the North American College in Rome, served as staff aide to the committee of U.S. bishops established by the Vatican to investigate seminary education in this country.

As head of the 860,000-member Pittsburgh diocese, Wuerl is expected to follow the strict constructionist style of Bevilacqua in administering church doctrine and laws.

The Philadelphia ceremonies in which Bevilacqua was installed to succeed Krol marked the first time in more than a century that the head of the historic archdiocese was present to pass on the office to his successor.