Almost one in four preschoolers lives in poverty, which makes the youngest Americans the poorest, too.

But a study shows tremendous variations across the country over the past two decades in poverty rates and trends.In Louisiana, four in 10 children under age 6 lived in poverty between 1992 and 1996. But in New Hampshire and Utah, it was under 12 percent.

The rate in Utah was 11.36, the lowest in the nation, and a decrease of 20 percent from 1992-96.

"I expected to see variation but not as dramatic variation as we found," said Neil Bennett, co-author of the study released Thursday by the National Center for Children in Poverty at Columbia University. "A fourfold difference between states . . . is a stunning difference to be reckoned."

The study took the average poverty rate from 1979 to 1983 and compared it with the average in 1992-1996.

California, Texas and New York - where nearly half the poor children live - saw increases of more than 20 percent each, which helped drive the national rate up 12 percent.

But there was wide variation in growth.

In Connecticut, the rate jumped 62 percent, bringing that affluent state close to the national average. Meanwhile, its New England neighbor Ver-mont saw a drop of 39 percent, producing one of the country's lowest rates.

In the typical state, the study found, about 30 percent of the change can be attributed to changes in the number of mothers who finished high school, the proportion of young children with single moms and the portion with at least one parent working full time.

Those factors varied widely by state, with some correlation to child poverty.

Connecticut, for example, had a 13 percent drop in the number of children with a parent working full-time. But that figure jumped 48 percent in Alaska, which saw a 23 percent drop in the young child poverty rate.

Connecticut officials suggested the state has too few poor children to create a statistically significant sample size. Its economy took long-er than many states' to recover from the recession of the early 1990s, but that also is true for Massachusetts, which had a much smaller increase in child poverty, said Kevin Loveland, director of family services in Connecticut.

"It is puzzling," he said.

In 1996, 5.5 million children under 6 lived in poverty, down from the 1993 peak but still much higher than in the early 1980s, when there were 4.4 million.

In 1996, the official poverty line for a family of four was $16,036 a year; for a three-person family, it was $12,516. But the families of almost half the young children in poverty earned less than half that.