Nathan Keyfitz, the director of Harvard's Center for Population Studies and a recent adviser to the United States Census Bureau on ways to accurately adjust its population count, said yesterday that a recent court ruling on census undercounts "may result in basic reinterpretations of the Constitution."

The Constitution says that the population shall "be enumerated.' "In the past, the Justice Department has interpreted the enumerated to be only those who were actually counted, without including the undercount as an official part of the census," Keyfitz said.

But a Chicago judge ruled earlier this month that the Census Bureau had missed a substantial portion of the city's Black population and ordered the Bureau to submit a "statistically defensible" method of including the undercount in its total.

"What I have discussed with the census bureau is a process that matches census files with other administrative files such as medicare and social security and may account for some who were missed by the census. People may often avoid the census for one reason, but that same reason may not prevent them from being registered on some other government files," Keyfitz said.

"The census has been especially inaccurate in enumerating the Black population," Keyfitz said, citing figures to show that in 1970, when the white undercount was 1.9 per cent, the black undercount was 7.7 per cent.

"Cities with high Black populations will be cheated, because the census may result in both less renumeration and perhaps a loss in representation," he added.

The census bureau has traditionally, after finishing its count, made estimates of the undercount through comparative examinations of old census reports, birth and death records, and immigration reports. "Now, though, the bureau is under pressure to find a way to make these estimates before the enumeration is complete, and somehow incorporate these figures into the count," census official Charles D. Jones said yesterday.