Ask a father how his baby is doing, and one of his first responses probably will be to recite how the child's weight and height stack up against the national averages, expressed in percentiles.

Now, those percentiles are being updated as part of the National Health and Nutrition Examination Survey, a $100 million federal project covering 40,000 people in 88 communities. The survey, which includes extensive three-hour physical exams and blood tests, began in 1988 and will be completed in 1994. The result, officials say, will be the most detailed look ever at the nation's collective health.

Data collected in the survey, referred to as NHANES III, will set national standards for height, weight and blood pressure, according to the National Center for Health Statistics, which oversees the survey. The information also will be used to estimate the prevalence of major diseases, nutritional disorders and risk factors based on, among other things, race and ethnic background, according to the center.

National health surveys since 1960 have shown that cholesterol levels are creeping up, that high blood pressure is a problem and that some groups face greater risks than others of iron-deficiency anemia.

The surveys have spurred action. High levels of lead in blood, for example, pushed the U.S. Environmental Protection Agency to require gasoline companies to eliminate lead as an additive, said Kurt R. Maurer, chief of survey planning for NCHS.

This time, health officials will get their first national look at how widespread AIDS is, he said. All testing and information is confidential, but in testing for AIDS the survey is going a step further and making it impossible to identify those with evidence of the human immunodeficiency virus, Maurer said.

The survey will include a special blood sample from each participant, Maurer said. Those samples will be frozen at the Centers for Disease Control in Atlanta. If, in five or 10 years, health officials want to test for a health condition not covered in the survey, they will be able to use the blood samples.

In the early 1980s, some samples from the 1976-80 study were made available for hepatitis testing, which had not been part of the earlier survey. "It showed that hepatitis has been more widespread than we had previously expected," he said.

Three teams are at work. One will finish in Philadelphia this month and then move to Winston-Salem, N.C. A team conducting a survey in Boston will move on to Owenton, Ky., and the third will soon finish in Providence, R.I., and travel to Arlington.

In physical exams, participants are being checked for everything from dental health to gallstones. Tests of hearing, lung capacity, heart functions, bone density -- used to spot the bone-thinning condition called osteoporosis -- and vision are included. Potential health problems can be referred to a participant's physician, Warren said. Each participant -- there can be several per family -- is paid $30 to $50.