Most households can expect to receive mail this week informing them that census forms are about to be sent to them. The 120 million actual forms are mailed next week, urging people to complete and return them by April 1. As much as census and local government officials want to guard against an undercount of the population -- the bureau estimates the national undercount was 1.4 percent in 2000 -- steps are also being taken to reduce the possibility of an overcount. One analysis last year, done by Temple University professor Eugene Ericksen, estimated the city of Pittsburghhad a net overcount of 752 residents in 2000 because of mistakes in counting the high number of college students and senior citizens in the city.