A mysterious temporary dip in Southern white birthrates a generation ago may have resulted from psychological shock from the Supreme Court's landmark 1954 decision banning school segregation according to three sociologist at the University of North Carolina.

In the 1950s, birthrates all over the country were rising and nowhere faster than in the states of the Confedaracy.

But suddenly according to Ronald Rindfuss, John Shelton Reed and Craig St. John in an article is the July 14 edition of Science magazine, white birthrates plummeted in 1955 in the South while continuing to rise in the North.

Later they rose again in the South, but the temporary drop has never been explained.

Rindfuss, Reed and St. John speculate the reason for the drop was uncertainty and fright among whites fearing that "their region's way of life was threatened."

As a result, they theorize, "fear for the future led some southerners to put off having children who otherwise would have been conceived during this period." The desegregation decision apparently "demoralized prospective parents" and encouraged the use of contraception and concellation of plans to have children, they say.

The drop in the birthrate was greatest, the three authors declared, the spring and summer of 1955, nine months to a year or so after the May 17, 1954 court decision.

The authors said that in 1956, after it became clear to southern couples that "that segregation would (in fact) continue for some time, that life would go on much as usual . . . that nothing much was going to change any time soon," couples began conceiving babies at a faster rate and the birthrate rose again.

Rindfuss, in a telephone interview from Chapel Hill, N.C., said that if their theory is correct, "If wide fluctuations in population" are caused by "little, discrete, concrete historical events" rather than only large measurable factors like economic and health conditions, "then it's going to be very difficult to predict future trends in fertility."

In Washington, Dr. Martin O'Connell of the Census Bureau population division expressed considerable doubt about the Rindfuss-Reed-St. John theory, "annual birthrate are notoriosly poor indicators in that they fluctuate widely," he said. "A change in one year means absolutely nothing."

O'Connell said only if a trend in birthrates continues for several years can it be considered significant. He said he would have "little faith" in any theory attempting to explain a downturn lasting only a few months.

St. John, in a telephone interview, said O'Connell's strictures might be valid if the study dealt only with a handful of states, but in fact it covered the entire Old South and also compated it with the rest of the country. Rindfuss said other possible explanatory factors in the 1955 southern downturn, such as Hurricane Hazel which ravaged the South at that time and possible economic downturns in the area, had been examined but found inadequate as explanations.

Rindfuss, Reed and St. John said black birthrates in the South had also turned down in the crucial months of 1955, though less than white, and speculated that black, too, faced uncertainty after the Supreme Court decision.