Responding to a challenge by city officials, the U.S. Census Bureau has upped its most recent estimate of Baltimore's population by more than 10,000 - an indication that the city's half-century loss of population could be coming to an end.

According to the revised census estimates, Baltimore's population as of July 1, 2001, was 645,305 - not 635,210, as the bureau reported in April.

The revised estimate, the first of the annual nondecennial calculations of populations, still represents a decline from the city's census 2000 count of 651,154.

But it shows that Baltimore's rate of population loss has dropped drastically from that of the 1990s, when the city lost more people than any metropolis in the nation.

Mayor Martin O'Malley - who directed city officials to challenge the bureau's original estimate, saying it was damaging his efforts to rebuild Baltimore - greeted the bureau's revision enthusiastically.

"I think it's terrific," the mayor said last night. "There are so many people out there who want the city to do well. You've got to show them we're making progress. We're doing better, much better."

Although cautioning he didn't have a "crystal ball," O'Malley said the revised figures gave him hope that Baltimore could join other older cities such as New York and Chicago in gaining residents after decades of decline.

"It seems like when cities make themselves cleaner and safer, they experience an increase in population," he said. "I have every reason to believe that's what's happening here."

Benefits in numbers

The benefits of the revised estimates could be more than psychological.

City officials were trying last night to determine how much more money in federal and state assistance the revised numbers might mean. They compiled a list of programs that use population as a criterion for support, including Community Development Block Grants, Head Start and Medicaid.

Covering the 15-month period from April 1, 2000, to July 1, 2001, the revised estimates show Baltimore lost 5,849 people since Census 2000 - or an average of 390 per month.

In the 1990s, the city lost 84,860 people - or an average of 707 people a month.

Using previous census estimates, officials have calculated that the rate of the city's population decline based on the revised 2001 estimate is its lowest in a decade.

The Census Bureau's original estimate indicated that the city had lost 15,944 people - or an average of about 1,000 a month.

The estimate - like that for thousands of other jurisdictions - was based on data about births, deaths, foreign immigrations, and the movement of people between jurisdictions based on information from the Internal Revenue Service.

Housing data

The revised estimate was "based on a consideration of data" on housing that the city submitted, said Lisa Blumerman, chief of the bureau's population estimates branch. The Census Bureau will post the revised estimate on its Web site in the next few days, she added.

City officials said their challenge, which they submitted in September, included detailed information on permits for new construction and the abatement of vacant housing notices.

Blumerman would not say whether the Census Bureau would be revising estimates for other jurisdictions. Bureau officials had said previously that its estimates are "for the most part reliable," but acknowledged that they contained "some degree of uncertainty."

In announcing in May that the city would challenge the Census Bureau's original estimate, O'Malley said he was "absolutely" convinced that the number would be revised. He said he expected the revision to show that the city's population was "at least the same" as in the 2000 census.

In a letter to O'Malley received this week, John F. Long, chief of the Census Bureau's population division, wrote, "Your involvement in the challenge process contributed to the improved accuracy of our estimates and is therefore very valuable to us."

Baltimore's population peaked at 949,708 in 1950 and has been declining ever since. Between 1970 and 2000, the city lost more than a quarter of a million people.

The Census Bureau's next population estimate, covering the period from July 1, 2001 to July 1, 2002, is due in the spring.