Isabel Wood Rogers, a teacher at the Presbyterian School of Christian Education in Richmond, was elected moderator of the Presbyterian Church (USA) as the denomination's General Assembly began its annual 10-day legislative session this week in Biloxi, Miss.

Rogers, who spent her recent six-month sabbatical from teaching working with the Richmond YWCA's program for battered women and rape victims, edged the Rev. Joan SalmonCampbell of Philadelphia by a vote of 325 to 323 on the fifth ballot.

Rogers, the sixth woman to serve as moderator of the Northern or Southern churches, which reunited in 1983 to form the present church, succeeds the Rev. Benjamin Weir, a missionary and former hostage in Lebanon.

With the elections and other preliminaries out of the way, the assembly turned to one of the major items before it, a controversial study document on Christian-Jewish relations, which has been six years in preparation.

Titled "A Theological Understanding of the Relationship Between Christians and Jews," the document calls on church members to "acknowledge in repentance the church's long and deep complicity in the proliferation of anti-Jewish attidudes and actions through its 'teaching of contempt' for the Jews. Such teaching we now repudiate, together with the acts and attitudes which it generates.

"It is agonizing to discover that the church's 'teaching of contempt' was a major ingredient that made possible the monstrous policy of annihilation of Jews by Nazi Germany."

The document notes that "small acts of disdain" by Christians can lead to "such horrors . . . . We pledge, God helping us, never again to participate in, to contribute to, or (insofar as we are able) to allow the persecution or denigration of Jews, or the belittling of Judaism."

But Presbyterianism's historic mission ties to the Arab culture of the Middle East made agreement on questions dealing with the Jews as resistant to consensus in the church as in the political sphere.

The Rev. Salim Sahiouny, head of the National Evangelical Synod of Syria and Lebanon, told the assembly committee studying the document, "It's about time to get over this feeling" of guilt. "The Holocaust is repeatedly practiced in the Middle East and other places."

Another section dealing with "the continuity and irrevocability of God's promise of land to the people of Israel" was criticized by Sahiouny. The Jews, he said "have rejected the covenant. God has not rejected them; they have rejected the covenant."

Moderator Weir complained that the paper could be an embarrassment to the United States and to Christians if it includes language that can be interpreted as promising Palestine to the Jews in perpetuity. A second study paper on Islam is also before the assembly.

An even hotter battle is expected over the selection of a new headquarters site for the merged church. After a detailed two-year study, the site committee recommended Kansas City as the headquarters.

But church, civic and political leaders pushing Louisville are scheduled to make flying visits to the Biloxi assembly today in a concerted effort to overturn that decision.

Meanwhile, Atlanta and Philadelphia, where some offices of the predecessor churches are currently located, also are seeking to stay in the headquarters sweepstakes.

The Rev. James Andrews, chief executive officer of the church, told commissioners, as delegates to the General Assembly are known, that the denomination has lost almost 200,000 members in the four years since reunion of the northern and southern branches.

Andrews, stated clerk of the church, said the denomination had 3,016,488 members in 1986, a drop from 3.2 million when the United Presbyterian Church (USA) and Presbyterian Church (US) combined in 1983. The denomination lost 40,738 members last year, Andrews said, adding that he expects to find within the next three weeks that membership will have dropped below 3 million.

Andrews said only a small part of the decline can be blamed on the reunion. Other reasons include a general decline in the nation's church membership and a more careful keeping of statistics.

Andrews said a part of the decline can be attributed to an increase in evangelical churches.