NEW BRUNSWICK, N.J. (AP) -- No one has tried to count them all. Not even the federal government, which is responsible for their well-being.

So how many children are working illegally in America?

On behalf of The Associated Press, a Rutgers University labor economist analyzed data from census surveys and other sources to estimate their number. The result: 290,200 children -- two-thirds of them 15 years or younger -- worked unlawfully in America last year.

Not all those children, more than two boys to every girl, are living a Dickensian nightmare. Some are teen-agers selling burgers and fries at the mall for more hours than the law allows.

Others, though, toil in jobs too dangerous for their years, or work during the very school hours designed to give them a chance at a future.

The study by Douglas L. Kruse, a labor economist at the School of Management and Labor Relations at Rutgers, represents the only comprehensive estimate of illegal child labor in the nation now available. If nothing else, Kruse said, the study makes a strong case for developing better data on the employment of children.

Because migrant laborers and very young child workers are particularly difficult for government surveys to pick up, the study may well leave thousands of child workers uncounted.

Nevertheless, it estimates that:

Of the 290,200 children illegally employed last year, 129,700 were 14 or 15 years old, and 59,600 were younger than that.

147,700 children work illegally in America in an average week.

Employers saved $155 million last year employing children illegally, rather than paying more to hire legal workers.

Children working in jobs the law declares too hazardous for their age were paid $1.38 an hour less on average than those who could be employed in compliance with the law. Children working illegally averaged $5 an hour.

While illegal child labor appears to have decreased since the 1970s, the number of boys and girls working in violation of the law has stabilized in the most recent period measured, 1995-97.

To put the estimates in context, the number of children working illegally is close to 4 percent of the 4.1 million children aged 12 to 17 who work in America during any given week.

Some industries were harder for Kruse to measure than others. Illegal home-based work, like sewing dresses outside the workplace, was not included in the illegal count since there was no accurate way to calculate how many kids were involved.

The study did estimate 13,100 children were working illegally last year in garment industry sweatshops, defined as businesses with a pattern of violating wage, safety and child labor regulations.

Agriculture, which relies heavily in some areas of the country on migrant workers, is also hard to examine.

To make an estimate, Kruse took the number of child labor violations the U.S. Department of Labor actually found in agriculture and extrapolated a figure for the number of children working illegally in that industry. This calculation assumes that the department polices agriculture as thoroughly as other areas of the economy. However, the AP has found that it does not, which makes Kruse's estimate conservative.

"Child labor laws for agricultural employment are much less stringent than for nonagricultural employment,'' Kruse noted. In some cases, kids under age 12 can work legally for commercial farms.

With those caveats, Kruse estimated 4,900 children worked illegally last year in agriculture, which includes both crop and livestock work. To put that in context, he figured 229,600 children aged 14 to 17, for which data are the most complete, were employed in the industry last year.

A figure for younger children in agriculture could not be calculated due to a lack of good data. AP reporters who visited farms saw scores of children under 14 at work.

To make his overall calculations, Kruse first examined employment data about 15- 16- and 17-year-olds in the Current Population Survey, compiled by the Bureau of Labor Statistics and the Census Bureau. He then compared the responses with federal and state labor laws to identify violations. Kruse combined 33 monthly surveys from January 1995 to September 1997 to get a large enough sample. Each survey looked at about 60,000 households.

To calculate how many younger children work illegally, Kruse used other data including the National Longitudinal Survey of Youth, and statistics on adolescent work-related injuries and death.

Examining data over time, Kruse estimated that illegal child labor decreased since the 1970s. However, in recent years, the decline has stopped. He found the number of 15- to 17-year-olds working in violation of federal law during an average school week has varied over the past 26 years:

156,000 in 1971-75.

169,000 in 1976-80.

100,000 in 1991-94.

For the most recent period, 1995-97, the number increased to 114,000. However, the statistical limitations of the study make it difficult to know if the increase is real.