For the third year in a row, the Southern Baptist Convention, the nation's largest Protestant denomination, has reported a decline in the number of baptisms.

While overall membership figures showed a 1 percent increase last year for a total of 14,486,403, baptisms in the strife-torn denomination were down by 5.6 percent. The rate of baptisms is a critical measure of the church dynamics because it is by baptism that new members enter the church.

Officials acknowledged that the overall membership figure is imprecise since there are no formal methods of clearing from church rolls persons who have drifted away.

"Some large churches have thousands of people on the rolls they couldn't find if they had to," said a church official who asked not to be identified.

The statistical report indicated that of the 14.5 million members claimed, 4.2 million "are reported as nonresident members."

In commenting on the decline in baptisms, the press release reporting church statistics noted that "in 1985 it took 41.3 Southern Baptist church members to win one person to Christ" in contrast to a ratio of 1 to 30.2 in 1975 and 20.3 in 1955. Conversion of others to Christ is viewed as the highest purpose of the denomination.

Church leaders would not comment on a possible link between the declining rate of baptisms and the bitter conflict in the church between moderates and conservatives over how the Bible should be interpreted that has gripped Southern Baptists in recent years.

In the latest developments in that controversy, SBC lawyers have asked a federal court to dismiss a lawsuit against the denomination brought by four lay persons after last year's annual convention. The plaintiffs, who were messengers, or delegates, to the convention, claim their rights were violated by controversial rulings of SBC President Charles F. Stanley. The rulings in effect denied moderates an opportunity to nominate persons to a key committee.

SBC attorneys, including former U.S. attorney general Griffin Bell of Atlanta, contend that the First Amendment guarantee of church-state separation bars federal courts from entering the dispute.

They also claimed that the dispute involves only "ecclesiastical representational rights" rather than monetary damages of at least $10,000 as is required by federal statutes.

The report of the denomination's 1985 statistics noted a 1.3 percent increase in Sunday school enrollment. It also reported that despite a slowing of membership growth, overall financial contributions last year increased 6 percent for a total of $3.89 billion, of which nearly 16 percent was earmarked for missions.