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.