Southern Baptist moderates today turned back efforts by fundamentalists to pull the 14.4 million-member denomination out of a 50-year-old multi-Baptist lobby and education office in Washington and in its place set up an exclusive Southern Baptist unit.

An independent Southern Baptist lobby would give the fundamentalists, who now dominate church leadership, the opportunity to press their views on such issues as school prayer and antiabortion legislation.

"I've kept an eye on what's been going on" with the Baptist Joint Committee on Public Affairs, the Rev. J. Steve Sells of Greensboro, N.C., said, accusing the multi-Baptist committee of associating with the anti-New Right lobbying group People for the American Way "and all kinds of abortion movements."

"We need to come back to our own representation" in Washington, Sells said, to applause.

Lynn Clayton of Alexandria, La., noted that the convention's new president, the Rev. Adrian P. Rogers, had "said we should work with other Christians. Surely this means other Baptists."

Southern Baptists are the largest of eight denominations in the joint committee and provide 80 percent of the budget as well as the current director, James M. Dunn.

Fundamentalists targeted Dunn more than two years ago for his involvement with People for the American Way, which the religious right has branded a secular humanist organization. Dunn also has lobbied and spoken against efforts to legalize prayer in public schools.

After the Southern Baptist Convention two years ago narrowly defeated an effort to pull the denomination out of the joint committee, Dunn cut his ties to People for the American Way. And when the convention reversed its position on school prayer, he refrained from speaking out on that issue.

Today's motion to withdraw from the joint committee caught Dunn and his supporters by surprise. After several parliamentary maneuvers to get it sidetracked were declared out of order, Clayton moved that the motion be referred to the convention's executive committee for study.

A majority of the delegates approved, which means the issue will come before the convention again next year, with the executive committee's recommendation.

Also today, the convention adopted a resolution authored by Dunn expressing "our abiding and unchanging opposition to the continuance of a United States ambassador" to the Vatican.

Phil Caskey of Stillwater, Okla., speaking in defense of Dunn, reminded delegates of that issue. "James does a superb job for us," he said to a smattering of applause. "James Dunn has been opposing diplomatic relations with the Vatican before it was a twinkle in President Reagan's eye."