A federal court ruled unanimously Monday that the Census Bureau's plans to use statistical sampling to supplement the 2000 Census violated federal law.

The bureau had hoped to use sampling to avoid a repetition of the 1990 Census, which missed 8.4 million people and counted 4.4 million either twice or in the wrong place while relying exclusively on traditional head-counting.Those who stood to gain by sampling included minority groups, whose members have been disproportionately undercounted.

The issue has achieved a heightened importance because census data are used to apportion House seats and draw boundaries for congressional districts. With House Republicans holding a razor-thin majority, both parties are acutely conscious of any question that might give one side an advantage.

Beyond the partisan wrangling, the issue is of grave concern to cities because some federal money is allocated on the basis of population.

The decision can be appealed directly to the U.S. Supreme Court, and the Clinton administration is expected to do so.

Proponents of sampling said they still hoped for a favorable decision from the Supreme Court. "Ultimately, it will be before the Supreme Court," said Rep. Carolyn Maloney, D-N.Y. "The nation needs an accurate count that includes everyone."