Dissenting parishioners of Alexandria's Good Shepherd Roman Catholic Church, is dispute with their bishop over Church authority, have formed a full-fledged church-within-a-church in order to assert what they see as their rights to help guide their church's affairs.

The $67,000 budget adopted at a membership meeting Saturday of the Good Shepherd group is intended to implement twin goals. The group, called the Good Shepherd Catholics for Shared Responsibility, will continue its own program of religious life, including its own system of religious education, Sunday masses and community service.

At the same time, they agreed to continue their efforts to secure "shared responsibility," a concept under which the right to lay members assume a greater role in church decision making.

The trouble at Good Shepherd began a little more than three years ago when Catholic parishes in Northern Virginia were separated from the Diocese of Richmond to become a separate diocese with Bishop Welsh, who tends to take a conservative view of the church, at the head.

At that time Good Shepherd was under the leadership of the Rev. Thomas Quinlan, considered a progressive. It had gained national attention as a model of a parish that had put into practice the mandates of the Second Vatican Council to involve parishioners in virtually every aspect of church life.

When Father Qinlan left Good Shepherd to return to Richmond, his successor, with the backing of Bishop Welsh, unilaterally rolled back some of the changes that had been made. The problems erupted when he sought to curb and ultimately to disband the democratically elected parish, council, which shared with the pastor responsibility for guiding the parish.

The council and a substantial number of parishioners countered by pledging to fight for a return to "shared responsibility." Several efforts at arbitration have thus far failed to resolve the dispute. An appeal from the dissidents now is before the Vatican.

For nearly 18 months, the dissidents have been gathering each Sunday for the contemporary style liturgies they favor, planned by members of their own group, as they had done under Father Quinlan's leadership. They have met in churches of other denominations or in amilitary base chapel, and the sacrament has been administrated by a priest from another diocese or from a Catholic shcool. Bishop Welsh has forbidden Arlington priests from saying mass for the dissidents.

They have instituted as well their own program of Christian education for their children and a separate youth program for teen-agers.

In adopting their $67,000 budget Saturday, the group earmarked $35,000 of it, for social development programs. They agreed that if their income fell short of expectations they would give half of what they did raise to such service project elsewhere. Projects suggested for support ranged from traditional charity work and antiabortion activities to support for the Equal Rights Amendment and movements challenging national nuclear energy policy.

Despite all these activities the dissenters say they still consider themselves members of Good Shepherd Parish. Some do, in fact, fulfill their Sunday mass requirement by attending their old church on a regular basis.

"We are trying to stay within the church," explained Regis Reynolds, current president of the Good Shepherd Catholics for Shared Responsibility council. "Otherwise we will be just like all the others who just left the church and accomplished nothing."

Recently, Good Shepherd's pastor, the Rev. Frank Mahler, removed a number of the dissidents from the church roles in part because of their financial boycott of the parish.

Reynolds, an army officer who says his position as head of the dissidents costs him about 25 hours of work a week, protested the action to Bishop Welsh. Reynolds also protested the problems that have arisen during funerals at the church where families of the deceased have requested participation in the funeral liturgy by persons related to the dissident group.

Father Mahler has on occasion balked at such participation.

Bishop Welsh responded to Reynold' protests by backing Father Mahler on both counts. "If you wish to use the facilities of the parish, you will have to accept the church's regulations," the bishop wrote.

In his letter to Reynolds Bishop Welsh suggested how reconciliation could be accomplished. In his reply, Bishop Welsh noted that Reynolds had addressed him as "our bishop." The Bishop urged the dissidents to "accept that fact" which, he said, "includes a response of obedience, which I pray you can all come to make."

The chorus of groans with which that line was greeted when Reynolds read Bishop Welsh's letter to Saturday's gathering of the dissident group was clear indication that the two sides claimed.