The governing body of the nation's largest Presbyterian denomination voted overwhelmingly yesterday to end a split that dates to the Civil War and reunite with the southern branch of the church.

Meeting in Hartford, Conn., the general assembly of the United Presbyterian Church of the U.S.A. voted 571 to 18 to merge with the the Presbyterian Church in the United States, whose assembly approved a similar motion earlier this month.

The merger plan, 13 years in the making, would reunite the two major streams of Presbyterianism in this country: the 2.4 million member UPCUSA and the 838,000 member southern church.

In addition to the vote by the national bodies of the two churches, the merger plan must still win the approval of two-thirds of the presbyteries, as local associatons of churches are called, of the UPCUSA and three-fourths of the PCUS presbyteries.

If the required number of presbyteries ratify the plan, the two churches will convene in a joint assembly next June in Atlanta to establish the unified church.

Despite the overwhelming vote of approval of the PCUS Assembly, church leaders report substantial antimerger sentiment in nearly a score of that denomination's 61 presbyteries.

Presbyterianism as an organized religion in this country is older than the nation itself, with the first presbytery organized in Philadelphia in 1706, and established as a national denomination in 1789, when the first general assembly was held.

The church split in 1861 at the beginning of the Civil War over questions of slavery and states' rights, and the PCUS body was formally established in 1865.

There had been some hope that the southern church would be a part of a 1958 union plan, which brought together the Presbyterian Church in the USA and a smaller group, the United Presbyterian Church of North America.

The southern church, which tends to be slightly more conservative theologically, was not yet ready to take such a step at the national level. But in some areas, particularly in the border states, cooperation of local congregations of the two churches flourished. In 16 such communities, including Washington, local church leaders anticipated reunion on a national level by forming union presbyteries.

Both ordain women to the ministry, but the UPCUSA has been somewhat more aggressive in its insistence on decision-making roles for women at all levels of church life. In fact, the women's organization of the church recommended against voting for reunion earlier this year because the merger plan did not include some of the gains that UPCUSA general assemblies have mandated for women, particularly the requirement that women must be included in the governing bodies of local congregations.