WASHINGTON — Big worries for the nation’s first high-tech census should have been obvious when tests showed some of the door-to-door headcounters couldn’t figure out their fancy new handheld computers.

Now, officials say, technology problems could add as much as $2 billion to the cost of the 2010 census and jeopardize the accuracy of the nation’s most important survey.

Census officials are considering a return to using paper and pencil to count every man, woman and child in the nation.

At more than $11 billion, the initial cost of the 2010 census was already the most expensive ever. Officials now are scrambling to hold down costs while trying to ensure the count produces reliable population numbers — figures that will be used to apportion seats in Congress and divvy up more than $300 billion a year in federal and state funding.

“What we’re facing is a statistical Katrina on the part of the administration,” said Rep. Carolyn Maloney, D-N.Y.

“Will they leave this mess for the next administration?” asked Maloney, a member of the House committee that oversees the census.

This was to be the first truly high-tech count in the nation’s history, with census-takers using handheld computers to track and tally the millions of Americans who do not return the census forms mailed out by the government. The Census Bureau plans to hire and train nearly 600,000 temporary workers to help.

But interviews, congressional testimony and government reports describe an agency that was unprepared to manage a $600 million contract for the handheld computers that will be vital. Census officials are being blamed for a poor job spelling out technical requirements to the contractor, Florida-based Harris Corp.

The computers proved too complex for some temporary workers who tried to use them in a test last year in North Carolina. Also, the computers were not initially programmed to transmit the large amounts of data necessary.

“This is a management problem. It’s an organizational problem,” Commerce Secretary Carlos Gutierrez said in testimony this month before the Senate Homeland Security and Government Affairs Committee.

Gutierrez, who oversees the Census Bureau, said officials there were unaccustomed to working with an outside vendor on such a large contract.

Census Director Steven Murdock acknowledged in an interview Tuesday that “communication problems” between census officials and Harris Corp. have resulted in “serious issues.”

But, he added, “My pledge is that we are going to have a complete and accurate census.”

Murdock, the former state demographer of Texas, was confirmed as census director in December. As an appointee of President Bush, he is not guaranteed to keep his job in the next administration, when the census will take place. Gutierrez is virtually certain to be replaced by the new president.

Harris Corp. was awarded a $596 million contract in March 2006 to supply the handheld computers and the operating system that supports them. The contract has since grown to $647 million, and could balloon by as much as $2 billion, according to a report this month by the Government Accountability Office.

Gutierrez and Murdock are considering several plans to scale back the use of the computers. Only one option would have door-to-door headcounters using them to enter census data collected from residents. The others call for a return to paper and pencil.

Murdock said Tuesday he wasn’t ready to put a price tag on the options. Gutierrez is expected to brief Congress early next month.

Initially, the computer system was to have had several functions:

* Workers would use the handheld computers to verify every residential address in the nation, a process that is crucial to ensuring an accurate count.

* They would use the computers to collect and transmit information from residents who failed to return the census forms mailed out by the government.

* The computer system would track and manage workflow for all field operations.

* Harris Corp. would provide technical support for the system.

Harris Corp. spokesman Marc Raimondi said the company is committed to working with the Census Bureau to resolve any issues involving the handheld computers or the operating system.

He also said the computers actually are easy to use, with a failure rate of less than 1 percent when tested in the field.

“After you spend about 30 minutes to an hour familiarizing yourself with it, it’s as easy to use as a modern cell phone,” Raimondi said.

The success — or failure — of the census could have widespread repercussions. The Constitution has required a census every 10 years since the first one in 1790. It is used to apportion the 435 seats in the House of Representatives among the states. And states and many cities use census data to draw legislative districts.

Population numbers are used to calculate billions in state and federal grants for transportation, education and other programs. Private businesses use census data to identify labor and consumer markets.

“It is a massive undertaking, and if it is not done right, it weakens the confidence in the data that is produced,” said Rep. Mike Turner of Ohio, the top Republican on the House subcommittee that oversees the census.

“The reality is, we have to do the census, we have to do it well it and Congress will need to fund it,” Turner said.