Gertrude Cleary is a faithful Roman Catholic who attends mass every day at Blessed Sacrament parish, just off Chevy Chase Circle NW.

At 71, she has lived through the two decades of tumultuous change produced by the Second Vatican Council, and she thinks they are just fine.

"I think it's wonderful now to have the mass in your own language, so people know what they are saying," she said.

The old days, when the priest said mass in Latin with his back to the congregation and people mumbled the Latin responses that few understood, have no appeal to her, she said, declaring, "You should understand as much as you can possibly understand."

Ever since the Second Vatican Council ended almost 20 years ago, the sweeping changes that it produced have been the source of unending controversy in the church.

Vatican II changed the way that Catholics worship, the way they deal with their non-Catholic neighbors, and redefined their duties as Christians. It took their church out of a forbidding fortress and thrust it into the midst of the problems of the world.

Last week, just before embarking on his sixth tour of Latin America, Pope John Paul II, in a surprise move, announced plans for an extraordinary synod of bishops from around the world to examine and evaluate the changes produced by Vatican II, "in the light of new needs," he said.

Vatican II was the brainchild of Pope John XXIII. There was a need, he said, to "open the windows" and update the church that increasingly had walled itself off from the rapidly changing world in which its people lived.

The council began in October 1962 and ended in December 1965. Some 2,860 bishops from around the world participated. The four sessions of about two months each were conducted in Latin, behind closed doors.

For parishes such as Blessed Sacrament, the changes flowing from Vatican II have been so integrated into daily parish life that even the priest, Msgr. Thomas Duffy, has to stop and think what the church was like before the council.

"Of course, the most obvious thing is the liturgy," he said, with the mass now in English instead of Latin and the altar turned around so that the priest faces the people.

In addition, more than 100 trained lay-men and women take part in masses, reading prayers and scripture, leading the congregation's responses and helping the priests distribute communion.

For her part, Gertrude Cleary believes that these changes have made Catholics "more mature."

"Since Vatican II, I think the church has been strengthened," she said.

She remembers that when her children, now adults, were being prepared for first communion they were warned that they had to fast before communion and "not even have a drink of water."

"To me, those were all man-made rules" that had little to do with her faith, she said.

A retired career woman whose -- husband's death at 43 had left her with three children to bring up, Cleary is pleased to see women taking a more active part in the church as lectors and communion ministers. She said that "in some places they have altar girls, but we don't do that at Blessed Sacrament."

She also likes the new style of confession, now called the sacrament of penance.

"It used to be just like a popcorn list. You'd recite: 'seven lies, two impure thoughts . . . . ' " she said. "Now, you go and sit down and talk to the priest and, of course, he doesn't try to be a psychologist but at least there's dialogue."

Council documents spoke of priests and laity together as the "whole people of God," who must share responsibility for their church. Elected parish councils and other structures now perform many functions that once were done by the priests.

At Blessed Sacrament there are committees to plan the liturgies, a committee in charge of the Sunday morning speaker series and a school board that sets tuition fees and teacher salaries and makes other decisions for the parish elementary school. A buildings and grounds committee keeps the church and school in running order. The whole parish council goes over the church's budget.

"Eventually, it all comes to me for my final approval, but unless something is very radically wrong, I usually go along with them," Duffy said. "Any significant policy question goes through the parish council."

There have been widely publicized conflicts in the Roman Catholic Church over parish councils, but vastly more parishes It is not unusual for a penitent to express remorse over prejudice or "a wrong attitude to another race. I'm not sure I heard that before Vatican II." -- Msgr. Thomas Duffy have welcomed the idea and quietly put it to work, moving from the old "pray, pay and obey" for lay members to "shared responsibility."

Some of the most significant achievements of the council are not visible within a local parish, but have had a major impact on the church on the national and world scene:

* Vatican II made it possible for Catholics to reach out to their "separated brethren" in other Christian churches, in the parlance of the council.

"When I was a child, I couldn't even go to a Protestant church. Now I can go to a Protestant church or a Jewish temple and be very comfortable," Cleary observed.

The interdenominational dialogue made possible by Vatican II's Decree on Ecumenism has opened the way for practical cooperation on projects ranging from sheltering the homeless to lobbying Congress.

* A council document absolving Jews, as a people, of responsibility in the crucifixion of Christ demolished the canard of Jews as "Christ-killers" and has been an effective weapon in battling anti-Semitism.

* Vatican II made it clear that working for social justice and peace is an integral part of being Christian, a teaching that is reflected in such major issues as the church's current controversy over liberation theology and in individual Catholic consciences.

"I see a much keener sensitivity to social issues" in hearing confessions at Blessed Sacrament, Duffy said.

It is not unusual, he added, for a penitent to express remorse over prejudice or "a wrong attitude to another race."

I'm not sure I heard that before Vatican II," Duffy said.

* The concept of "collegiality," of bishops consulting to reach a decision rather than relying on a single authority figure, has proved a remarkable model for the American Catholic bishops in developing their widely consultative pastoral letters on nuclear warfare and on the economy.

In addition, the most influential bishops govern their dioceses today in a collegial, consultative style, even though both church tradition and canon law considers bishops "God in their own diocese."

* The development of the National Conference of Catholic Bishops as a strong force for leadership of American Catholics, and counterpart organizations in other countries, has its roots in Vatican II's actions.

Some critics blame a vague "spirit of Vatican II" for problems ranging from the precipitous decline in attendance at mass to the alarming shortage of priests and nuns. But Catholics, along with the rest of the population, live in a world that has been rocked by social change in the last 20 years, a world of growing secularism, feminist and sexual revolutions, post-Watergate and post-Vietnam jaded idealism, antiinstitutionialism and the ascent of technology.

Some of the thorniest problems that the church faces today, however, were not discussed by Vatican II. Birth control and clerical celibacy were specifically excluded by Pope Paul VI from the council's deliberations. Nor was the role of women ever considered as a separate issue.

The synod summoned by John Paul will have no more than 150 participants, including the 101 presidents of bishops' conferences around the world, the heads of Vatican Curia offices, patriarchs of Eastern Rite chuches and the heads of three religious orders.

The synod can neither overturn the actions of the Second Vatican Council nor, on its own initiative, enact new measures, but is expected to make recommendations to the pope.