A federal judge ordered the Census Bureau today to adjust what he described as a "disproportionate undercount" of the population of New York City and New York State.

"I hold that there has been an undercount of the population of New York City and New York State that is disproportionate to the national average," Judge Henry F. Werker said. "Census Bureau mismanagement . . . contributed to the undercount."

Werker's 34-page decision restrained the Census Bureau from certifying the state population totals to the president on Dec. 31, as required by law, and ordered the bureau to come up with a plan for adjusted figures.

A federal judge in Detroit made a similar ruling earlier this year. The government is appealing that ruling.

New York contended in its suit that the count of city residents was at least 800,000 persons low, and that there were an additional 200,000 residents uncounted in the rest of the state.

The suit contended a major reason for the disparity was that census-takers were afraid to venture into minority enclaves and poor neighborhoods.

The judge ruled the use of "reasonable and scientifically valid statistical, survey or sampling procedures to adjust census figures for the differential undercount is constitutionally permissible." He also declared that the statutory deadline of Dec. 31 for reporting to the president was "directory and not mandatory."

The Census Bureau generally had claimed the only accurate way to check its figures was to send people door-to-door to count residents. It said it could not do that by the Dec. 31 deadline.

Werker directed the Census Bureau to report to him within 30 days its plan to make the adjusted count, adding that he would not stay his decision pending an appeal.