Census Switch Worries Some

The figures also are used to draw the boundaries of state voting districts. Then there's the $300 billion a year in federal grants allocated according to census results, not to mention the data's importance to state and local government planners as they consider construction of roads and schools.

"The implications of an undercount would be disastrous," Vargas said. "It would mean we'd be denying fair representation and resources to the people who need it most -- and who are undercounted precisely because they face those challenges."

Already the late switch in procedures forced the bureau to drop a dry run of the follow-up interview process from the "dress rehearsal" it traditionally holds two years before the actual count, depriving the bureau of the insight into potential glitches it usually gets at this stage of the preparations.

Pushing the census back from its scheduled start in April 2010 was not an option: To meet the legally mandated December 31, 2010, deadline for delivering population counts to the president, census activities must be carried out according to a strict schedule.

Even under the best of circumstances, the task of counting the more than 301 million residents of the United States can seem impossibly daunting. The scale and technical complexity mean that even minor hiccups can spiral into major crises.

A report last month by the U.S. Government Accountability Office, for instance, noted that if workers conducting the 2000 Census had spent just one minute more at each household during follow-up visits it would have added almost $10 million to the overall cost.

The GAO report, as well as a similar report last month by the inspector general of the Commerce Department, also noted that such other crucial elements as a new strategy for sending out second mailings and dealing with late mail returns were not included in the dress rehearsal.

Elements that have been tested, including a plan for field workers to use the hand-held devices to verify the bureau's address list in advance of the census, have continued to experience significant problems.

"The Bureau has taken important steps towards managing the changes it plans," the GAO report concluded. "Yet much remains uncertain."