On Sunday the Rev. Nancy Hastings Sehested preached her first sermon as pastor of Prescott Memorial Southern Baptist church in Memphis and won a unanimous vote of approval from the congregation.

Last night the Shelby Baptist Association of Memphis-area Baptist churches voted 80 to 20 to expel Prescott Memorial for naming a woman pastor.

The congregation is the first Southern Baptist church in Tennessee to choose a female pastor and is one of only four or five in the nation that has a woman as senior pastor.

Sehested, 36, who followed her father and grandfather into the Southern Baptist ministry, was selected in August from a field of 80 candidates as pastor of the 235-member Prescott Memorial, a progressive congregation in this bastion of Baptist conservativism.

Ordination of women has been a continuing point of controversy in the denomination, which has 14.6 million members. A sacred principle of Baptist practice has been the belief in the unqualified right of each congregation to ordain and to call its own pastor without interference from a regional or national body.

But in 1984, as fundamentalist forces continued their efforts to wrest control of the denomination from moderates, the annual convention adopted a resolution holding that the Bible bars women from becoming pastors because of Eve's role in tempting Adam to sin in the Garden of Eden.

That Prescott Memorial should call a woman pastor is "strictly out of order, completely out," said the Rev. Vaughn W. Denton of Kirby Parkway Church in Memphis. At the Sept. 21 meeting of the Shelby Baptist Association, Denton demanded that Prescott Memorial's "doctrinal soundness" be investigated.

The results of that investigation were aired at the association's hour-long meeting last night. The group rejected a proposal to postpone action on expelling, or "disfellowing" Prescott Memorial.

The church continues to be a member of the Southern Baptist Convention and the Tennesee Baptist Association.

""We've never had a lady pastor before . . . . We accept the Bible as totally infallible and inerrant. Many places in scripture talk about the services of women and their place in church, but the Bible never mentions a woman being called to pastoral leadership," Denton said in a telephone interview.

"We didn't set out to call a pastor who was a woman or who wasn't a woman," said Tom J. Walsh, Jr., vice chairman of Prescott's board of deacons. Over the period of a year the church considered 80 applications, winnowing them down to three men and three women finalists of whom Sehested was judged "the one most qualified," he said.

Sehested, a native of Texas who graduated from City College of New York and Union Theological Seminary, is one of a handful of Southern Baptist women nationwide to serve as senior pastor of a church in the denomination. She heads what is by far the largest congregation. The others serve mission churches or other tiny operations.

In the strongly evangelical Southern Baptist denomination, mission churches in developing neighborhoods often have been growing areas of the church. The denomination's home missions board has poured millions of dollars into starting mission churches. In 1985, however, the board announced it would not fund mission churches that employ women pastors.

Between 450 to 500 Southern Baptist women have been ordained. Most serve as chaplains or in education or music ministries, or they grow frustrated and turn to another profession.

Prescott Memorial, located across the street from Memphis State University, was the first Baptist Church in Memphis to accept blacks as members and the first to ordain women as deacons.

Walsh said one of the questions put to the deacons by the association committee investigating "doctrinal soundness" was, "Did we have a scriptural basis for calling a woman" or "whether we do these things just to irritate people."

"If she'd been a man, she'd have had one of the better pastorates right away," moderate leader Walker L. Knight said of Sehested, who has been associate minister of Oakhurst Baptist Church in Decatur, Ga. Knight edits the Decatur-based SBC Today, unofficial publication of moderates in the church.