After decades of unity efforts, the nation's mainline Protestant churches face rising tensions between conservative and liberal wings in an ecclesiastical parallel to the liberal-conservative battle waged last fall in the political arena.

The United Presbyterian, Southern Baptist, Lutheran Church-Missouri Synod, United Methodist, United Church of Christ and Episcopal churches are all contending with left-wing polarizations that drain both time and resources from their central tasks and in some cases threaten outright schisms.

Although schism is not uncommon in the history of the Christian church, the splitting of a denomination, with its accompanying bitterness and pain, is a step most Christians dread, and contemplate only as a last resort.

Unofficial conservative caucuses have existed for years in most major denominations, some of them sufficiently well-organized and financed to be able to flood their churches and the news media with their publications.

They tend to have similar concerns, regardless of their denomination: criticism of church involvement in civil rights and other social issues; opposition to expanding the role of women in both church and society; opposition to church union efforts, including participation in the National Council of Churches and World Council of Churches. Their goal has been to turn the church back to a more pietistic, orthodox type of Christianity.

The threat of schism permeated the United Presbyterian Church's General Assembly, which concluded its annual 10-day session yesterday in Houston. Even before the annual national assembly, nearly 70 congregations had already left the 2.5 million-member denomination because of deep differences over theology, social action and the role of women.

Whether the General Assembly's reaffirmation of the Christian church's traditional view of Jesus as "truly God and truly human" will prevent further defections by the church's conservative wing remains to be seen.

The nation's largest Protestant denomination, the 13.6 million-member Southern Baptist Convention, faces its most serious schism threat in decades next month when Biblical fundamentalists will seek to wrest control of the denomination from the moderate forces that have guided it.

The Lutheran Church-Missouri Synod experienced schism six years ago when moderates, who could not subscribe to the literal interpretation of the Bible demanded by the church president, pulled out and formed the American Evangelical Lutheran Church. Now the Missouri Synod faces further strife at its July convention, as the retiring president, the Rev. Dr. J.A.O. Preus, has publicly challenged the orthodoxy of one of the most popular candidates to succeed him. Preus has also demanded that his 2.7 million-member denomination break fellowship with a somewhat more liberal sister Lutheran body, the 2.3 million-member American Lutheran Church.

Even the United Church of Christ, among the most liberal of mainline Protestant denominations, faces a challenge at its General Synod in late June from a conservative caucus seeking to reverse the church's earlier stands on abortion, homosexuality and other issues.

The United Methodist Church managed to avoid any formal moves toward schism at its quadrennial General Conference last year, but there is growing criticism from an unofficial, Biblical conservative group within the church called the Good News Movement.

Conservative Episcopalians, who disapproved of their denomination's decision to modernize the liturgy and open the priesthood to women, split from the church to form their own churches, some of which have in turn splintered into smaller churches in the five years since the original schism.

Church historian the Rev. Dr. Martin Marty of the University of Chicago, one of the leading observers of the American religious scene today, sees the battle between conservatives and liberals in the nation's churches, in part at least, as reflecting "a general mood in the country."

"Most anybody I know is somewhat more conservative today than a few years ago," he said.

In the United Presbyterian Church, the liberal-conservative polarization was most sharply focused several years ago when the church ruled that candidates for the ministry who opposed ordination of women could not themselves be ordained. Subsequent legislation two years ago by the church's General Assembly, requiring every local congregation to elect women to the session, as a Presbyterian congregation's governing body is called, increased discontent among conservatives who take literally St. Paul's injunction for women to "keep silent" in church.

But the issue that raised cries of "apostasy" and raised the most serious threats of schism was the decision by the local National Capital Union Presbytery two years ago to accept the credentials of a Rockville pastor, already ordained in the United Church of Christ, whose answer to a question about the divinity of Christ failed to satisfy some orthodox Presbyterians.

When the Rev. Mansfield Kaseman, 41, was asked if he believes that Jesus is God, he replied, "No, God is God." The presbytery nevertheless overwhelmingly voted him into the presbytery, taking into account both Kaseman's record of more than a decade of dedicated ministry in Florida and New England and the vast differences in theological terminology with which basic Christian beliefs may be expressed.

Although Kaseman, in subsequent explanation of his views, said that "Jesus is one with God," conservatives twice appealed his acceptance into the presbytery, but the church's highest court ultimately upheld the presbytery's action.

For some conservatives, already dismayed by the direction their church was taking on social and ecumenical issues, the issue of doctrinal integrity became a compelling reason for leaving. The Rev. Dr. John Gerstner, retired professor from the denomination's Pittsburgh Theological Seminary and a counsel to those appealing the Kaseman endorsement, declared his denomination apostate, that it had abandoned the faith.

"The United Presbyterian Church doesn't exist as a Christian church anymore," said Gerstner, revered by many in the denomination as one of its patriarchs.

Earlier this week, the General Assembly added to its already thick book of confession, which includes all of Christendom's historic creedal statements, the reaffirmation that "Jesus is one person, truly God and truly human. This mystery of God's grace in Jesus Christ, which can be experienced and proclaimed but never fully explained, is what ties Christians together in a common faith and life across the centuries."

But even before the General Assembly took this action, Gerstner had announced plans for a gathering of all interested dissidents to be held June 11 in Pittsburgh, to consider whether or not they would split.

Of the nearly 70 congregations that have wthdrawn, some have joined other, more conservative Presbyterian or Reform denominations that dot the Prostestant landscape, the fruits of earlier schisms. One group of dissidents took steps in March to form yet another small denomination, tentatively called the Evangelical Presbyterian Church.

One formidable obstacle to Presbyterian schism is a ruling adopted last year, in anticipation of the rebellion that has since boiled up, specifying that the property of each local Presbyterian church belongs not to the congregation but is held in trust for the denomination. If history is any guide, congregations determined to leave the fold can be expected to test that ruling in the civil courts.

Dr. William P. Thompson, the chief executive of the United Presbyterian Church, believes that further defections from his church will be miniml. He pointed out that "the churches which have already withdrawn are the ones which have been peripheral in the life of our church," and except for "a couple of large ones," have not been the big and vigorous churches of the denomination.

If it is the conservatives in Presbyterianism who are departing from the mainstream of the church, the opposite is true in the giant Southern Baptist Convention. there it is the moderates -- southern baptists don't use the word "liberal" -- who see themselves, in their worst nightmares, being forced out of the church by conservative-fundamentalist forces, which in the last three or four years have been moving into power in the denomination.

The battleground of the Southern Baptists is the Bible, or as the fundamentalists put it, "Biblical inerrancy," the view that everything in the Bible is literally true; that God literally created the world in seven 24-hour days; that Jonah literally traveled intact in the belly of a whale.

Many in the church, including the faculty of the denomination's six theological seminaries, agree with the fundamentalists that the Bible is indeed inspired by god, but that its wisdom is sometimes expressed in allegory, myth and poetry; that every word is not to be taken literally.

The inerrantists, under the banner of a group called the Baptist Faith and Message Fellowship, have made great headway with an ecclesiastical loaded question. Their "Do you believe in the Bible?," which they have made the litmus test of orthodoxy, admits no theological nuances.

Typical of their approach is an article in the current journal of the Fellowship offering a $1,000 reward to anyone who can elicit from a seminary president answers of "'yes' or 'no' with no other comment" to six questions about the Bible, such as, "Do you believe that God breathed every word of the original Bible and there were no erros of any kind in the original Bible . . .?"

With the aid of highly sophisticated techniques borrowed from secular politics -- techniques mainstream Baptists condemn as inhibiting the Holy Spirit -- the Baptist Faith and Message Fellowship has managed to capture the powerful presidency of the Convention for the last two years. The last two years. The Southern Baptist Convention's current president, the Rev. Bailey Smith, is best known to the nation for remarkng during a New Right political rally last summer that "God doesn't hear the prayers of a jew," which embarrassed and outraged moderates in the denomination.

He is being opposed for the presidency by a candidate of the moderates, Dr. Abner McCall, a former judge of the Texas Supreme Court who has just retired as president of Baylor University. The challenge marks the first time in the recent history of the Southern Baptist Convention that an incumbent is being opposed in the middle of what is normally a two-year presidential term.

Moderate forces took the unprecedented step of fielding a candidate to oppose smith not so much because of the anti-Jewish remark -- for which he has since apoligized, if not recanted -- but because of Smith's proposed appointments to a crucial committee of the denomination that has the ultimate power to shape not only all national boards of the denomination six theological seminaries as well.

Smith maintained that his appointees were "representative" of the range of Southern Baptist views. But his moderate critics, in the words of a leading Houston pastor, the Rev. Kenneth Chafin, have charged that he "stuck with his fundamentalist friends and representatives of a handful of churches who live on the right wing of the convention."

The showdown between moderates and the fundamentalist Biblical inerrantists is expected at the SBC's annual convention, to be held in Los Angeles next month. "We feel it's going to be the most significant convention [of the SBC] in this century," said W. C. Fields, the denomination's director of public relations. "It will determine the direction for many years of missionary and evangelism work. It can drastically change our growth pattern," he said. Ever since the post-World War II era, the evangelically agressive Southern Baptists have been the fastest growing church in mainline Protestantism.

Historian Marty, whose own liberlism prompted him five years ago to abandon the Luthern Church-Missouri Synod in which he was raised for the more progessive American Evangelical Luthern Church, finds hope for the churches in the present turmoil. "It reminds me of the story about the village atheist who, when the church caught on fire, led the bucket brigade. When they asked him why, he said, 'It was the first time something exciting was going on in the church.'"

This seasonhs controversy, said Marty, "is a tribute to the fact that there's life stirring there."