The Rev. John R. Keating, the Catholic bishop of Arlington who had presided over the explosive growth of his Northern Virginia diocese, died in Rome early yesterday morning of a heart attack, two days after he had a private audience with Pope John Paul II. He was 63.

Keating, a strong and often controversial supporter of the pope on such issues as contraception, abortion and women's ordination, was in Rome to report to the pope on the state of his parish, a duty every diocesan head must fulfill every five years.

During Keating's 14-year tenure, the diocese -- which stretches as far south as Fredericksburg and to the West Virginia border -- nearly doubled in membership, from 188,000 to 325,000. The growth was driven by suburban development and the influx of immigrants from Central and South America.

Since 1983, the bishop opened more than 20 new churches in six new parishes and opened seven new elementary schools, with an eighth scheduled to open this fall in Stafford County.

Keating had arrived in Rome on Monday with more than 20 other regional bishops, including Washington Cardinal James A. Hickey and Baltimore Cardinal William H. Keeler, and was to stay through Friday. The two-week visit was to include a private session and a special Mass with the pope, prayers at the tombs of the apostles Peter and Paul and meetings with the various departments of the Vatican, said the Rev. William E. Lori, auxiliary bishop of Washington who is with the group in Rome.

"I was shocked and saddened to learn of Bishop Keating's death," Hickey said in a statement read by Lori. "He was a strong and loving pastor of souls, a faithful servant of the Lord and the Church, an expert in canon law, a good neighbor and a good friend."

Keating appeared to be fine during a meeting Saturday with the Congregation for the Clergy, one of the Vatican offices, Lori said. Keating had dinner with friends Saturday night and reportedly was last seen alive returning to his quarters at the residence of the Oblate Fathers of St. Francis.

Keating's personal physician told the Arlington chancellor, the Rev. Robert J. Rippy, who was accompanying Keating, that the bishop "had significant heart problems," according to a statement released by the diocese. That information was not general knowledge, said Michael Flach, editor of the Arlington Catholic Herald, which released the statement.

Yesterday, news of Keating's death traveled quickly through local parishes.

"It's a sad day," said the Rev. Dominic P. Irace, rector of the Cathedral of St. Thomas More, the bishop's seat in Arlington. Irace got a call about the bishop's death at 6 a.m., in time to make an announcement to the 4,000 parishioners attending four Masses yesterday morning.

"The people were just in shock," Irace said. "He was 63 years old and the picture of perfect health who had never been sick." Irace said that he was unaware of any health problems and that Keating "was a person who took care of himself." The bishop had scheduled a seminar in April to talk with priests about keeping healthy and taking time off to rest, Irace said.

Keating was the second bishop of the diocese of Arlington, which Rome broke off from Richmond in 1974. In addition to opening new parishes and schools, Keating had become known nationally for his ability to attract young men to the priesthood -- some from other parts of the country -- at a time of a general priest shortage. Keating ordained 84 priests, peaking at 13 in 1996, an average of five or six a year while other dicoceses might ordain one or two, Flach said.

Despite such successes, Keating and his supporters often were locked in disagreement with many Catholics over his conservative doctrinal stances.

In 1994, he created an uproar when he became one of only two bishops in the United States to refuse to allow girls to serve on the altar -- despite papal approval of the practice. A recently formed group, known as Call to Action, put pressure on Keating, but he never relented.

"People's {greatest} frustration was not with the policy but that they weren't being heard," said Marguerite Carroll, a member of Good Shepherd Catholic Church in Mount Vernon and mother of two girls -- 8 and 11 the time -- who thought it "unfair" that girls could not be altar servers.

Two years later, Keating angered Latino members at St. Thomas More by supporting Irace's insistence that all religious education classes be taught in English. And despite pleas from some Catholics that their parishes return to the traditional Latin Mass, eliminated from general use in the 1960s, Keating never allowed it -- driving many Virginia Catholics to Washington churches offering a Latin Mass. Keating was born in Chicago on July 20, 1934, and graduated from seminaries in Illinois and the Gregorian University in Rome, where he also completed post-doctoral studies in canon law. He was ordained a priest in 1958 and served in various capacities in the Archdiocese of Chicago. He was interim administrator after the death of Cardinal John Cody in April 1982 and until the installation of Cardinal Joseph Bernardin four months later. Keating was appointed second bishop of Arlington on June 7, 1983, succeeding the Rev. Thomas J. Welsh, who became Bishop of Allentown, Pa. Finding a replacement for Keating could take three to nine months, said Bill Ryan, spokesman for the Washington-based National Conference of Catholic Bishops. Archbishop Agostino Cacciavillan, the pope's representative in Washington, will gather names of potential successors and submit them to the Vatican, from which the pope ultimately will choose one, Ryan said. CAPTION: Roman Catholic Bishop John R. Keating of Arlington oversaw a diocese that nearly doubled in membership during his tenure, from 188,000 to 325,000.