The Census Bureau overlooked at least 30,000 D.C. residents in its 1990 count because it missed more than 10,000 of the city's dwellings, as well as dormitories at several major universities, District officials said yesterday.

If the city is correct and its challenge to the Census Bureau's preliminary data is upheld by the bureau, the District's 1990 population will be at least 605,000, not 575,000, as the bureau estimated last month. That would still mean, however, there are about 30,000 fewer Washington residents than in 1980, when the Census Bureau counted 638,432.

The issue is critical for the city because funds for such federal programs as employment training and low-income housing assistance are allocated on the basis of population. City officials estimate that the District loses $200 to $800 for each resident it loses.

Using voter registration and tax records, visits by city personnel and other methods, District officials concluded in a formal challenge filed Monday that the Census Bureau missed 10,289 of the city's 281,900 apartments, condominium units and single-family homes.

At least one dwelling was overlooked on each of 1,242 of the city's 5,125 blocks, according to Deborah Maiese, research manager for the District's Office of Policy and Program Evaluation. And 470 blocks each had at least five overlooked housing units, she said.

"It's very hard to understand," said Maiese, when asked to explain how the Census Bureau could have missed so many housing units in the city. Census officials in Charlotte, N.C., the regional office responsible for the District's count, could not be reached for comment yesterday about the city's challenge.

Maiese said the District acknowledges that not all of the missed housing units are occupied. But using Census Bureau data for likely vacancy rates and the average number of people per housing unit, census takers probably missed roughly 21,000 people in the 10,289 units, Maiese said.

Further, the Census Bureau missed 12,376 beds at boarding homes, homes for the elderly and the mentally retarded and dormitories at Howard, Gallaudet, Catholic and American universities, Maiese said. It was "fair to assume," Maiese said, that these facilities were operating at 90 to 95 percent capacity.

Altogether, she said, slightly more than 30,000 District residents were missed in these various types of housing. Maiese added that the Census Bureau may have missed even more, depending on how it estimated the number of homeless people and illegal aliens.

Across the country, 5,337 local governments -- nearly 14 percent of the total 39,276 jurisdictions -- challenged the preliminary census figures by Monday, which was the deadline the bureau had set for responses.

Census Bureau Director Barbara Everitt Bryant told a congressional subcommittee yesterday that virtually all of the 50 major cities had contested the results. Of those, 33 cities had challenged 500 or fewer blocks, and seven cities had contested 2,000 or more blocks.

She argued that many of the discrepancies were the result of coding errors and would be easily resolved.

Staff writer Barbara Vobejda contributed to this report.