In a departure from tradition, the president of the Southern Baptist Convention has appointed a professional parliamentarian to guide him during what is expected to be another volatile annual meeting of the country's largest Protestant denomination next month in Atlanta.

A controversial ruling on parliamentary procedure by the Rev. Charles F. Stanley, president, during last year's convention in Dallas has led to two lawsuits that are still hanging over the church.

Stanley, a conservative, last year ruled out of order an effort by moderate messengers, as delegates are called, to amend nominations to a key committee. One effect of Stanley's ruling was to strengthen conservatives' control over the Southern Baptist Convention, a trend that has been the source of controversy in the church for almost a decade. Subsequently, several moderate lay Southern Baptists filed suits challenging the parliamentary decision in both federal and state courts. Though the church's constitution does not provide for a parliamentarian at the massive annual conventions, Stanley named C. Barry McCarty of Jarvisburg, N.C., a former vice president of the American Institute of Parliamentarians, as one of three parliamentarians for the Atlanta convention.

Stanley's other parliamentary aides will be the Rev. James T. Draper Jr. of Euless, Tex., and the Rev. John Sullivan of Shreveport, La. Draper is a past president of the church, strongly identified with the conservatives. Sullivan is a widely known pastor who is generally perceived not to have taken sides in the conservative-moderate controversy. McCarty is a Churches of Christ pastor who is active in Republican politics and has been a spokesman for right-to-life groups.