WASHINGTON, D.C.: The Supreme Court unanimously ruled today that the 1990 census, despite an admitted undercount by the Census Bureau, should not be changed. More than two dozen major cities and counties -- including New York, Los Angeles, Chicago and Atlanta -- had challenged the count, charging that a significant underrepresentation of minorities had cost the cities hundreds of millions of dollars in federal aid. Officials in Wisconsin, which stood to lose a seat in the U.S. House of Representatives to California if the census had been revised, were relieved by the ruling. Money may have been the motivation for the suit, but the big cities argued the undercount abridged their citizens' constitutional right to an equal vote. The Court ruled that the Bureau of the Census made an "extraordinary effort" to count fairly, and that the secretary of Commerce, who oversees the bureau, acted within his authority in accepting the figures. The Court said the Constitution, charges Congress with conducting an "acutual enumeration" of the population every decade, and that responsibility was reasonably met. The Commerce Department estimates that it missed about 1.6 percent of the population, but about five percent of blacks and Hispanics.