WASHINGTON — In a growing number of classrooms around the country, 4 is the new 5 and preschool the new kindergarten.

Hoping for a future payoff of better schools and sharper students, states are aggressively expanding publicly funded programs to the youngest students - 4 or even 3 years old.

And eschewing play-oriented day care, states are setting new academic standards, including class sizes and teacher credentials, to provide higher quality education before the first day of kindergarten.

Led by states such as Florida, Maryland and North Carolina, enrollment in public pre-K by 4- and even 3-year-olds jumped 40 percent from 2001 to 2006.

Excluding federal Head Start programs for poor children, the pre-K landscape now spans 38 states and covers nearly 1 million children, according to the National Institute for Early Education Research at Rutgers University.

The academic approach to pre-K made a believer out of Ronda Benjamin, who said her son, Terrence, had a bad attitude and couldn't recite the alphabet when he enrolled as a 4-year-old this fall at the Greenbelt Children's Center in Maryland. The center is a private pre-school near Washington that receives state support.

"Right now, he can write his ABCs. He knows how to count up to 25. He can read little words like 'cat' and 'rat.' (And) he's not as aggressive as he used to be," Benjamin said as Terrence sat nearby working on letter sounds. "He's doing better now that he's here."

It's not only such short-term benefits that advocates of publicly funded pre-K are counting on. They point to studies that suggest students who spend significant time in pre-K are likelier than their peers to behave in school, graduate from high school and be productive citizens.

"A good pre-K program has a chance to change the climate in a lot of schools, to make schools safer places, to really reduce disruptive behavior in classrooms and benefit all children," said Steve Barnett, director of the Rutgers institute.

Skeptics agree pre-school programs can have long-term benefits for low-income children who might not otherwise be exposed to enriching experiences found in more affluent homes. But they say proponents overstate the benefits. And they challenge the wisdom of devoting dollars for richer kids whose learning gains, they say, are not nearly so dramatic or long lasting.

"Quality pre-school gives a lasting boost to children from poor families," said Bruce Fuller, director of the Policy Analysis for California Education, an independent policy research center based at University of California-Berkeley and Stanford University. "But middle-class children only benefit slightly and by 5th grade, the effects have washed out."

Academic arguments aside, many states view pre-school as an attractive place to spend taxpayers' money. Several states, including Iowa, New York and Oklahoma, either offer schooling for most 4-year-olds or are in the process of doing so, Barnett said.

Nationally, public pre-K serves about 3 percent of all 3-years-olds and 30 percent of all 4-year-olds, slightly more than the number of children in Head Start, the federal program started 40 years ago for the country's poorest children, according to the institute.

Though offered at some level in many states, pre-K attendance is not mandatory. All but eight states, in fact, do not require children to attend school until age 6, according to the Education Commission of the States.

A parade of Democratic presidential candidates have added their support, proposing billions so states can create or widen quality pre-kindergarten programs that would give tens of thousands more 4-year-olds a chance to go to class.

In Maryland, pre-school enrollment rose from about 11,000 in 2001 to more than 24,000 in 2006. The state funded the expansion by increasing aid to school systems, paid for in part by raising the cigarette tax.

The $100,000 the Greenbelt pre-school gets each year helps defray tuition costs for low-income families, said Flora Gee, the center's director. It also helps pay for an array of extras, including field trips, music instruction and computers, that allow the school to tailor learning strategies for specific children.

"You're individualizing instruction, and that's the mark of a really good teacher and a really good program."

But not every state is willing to pay extra.

California voters rejected a massive expansion of state-funded pre-school in 2006 after opponents, including Gov. Arnold Schwarzenegger, said it would cost too much and require a tax increase.

TIPS FOR CHECKING OUT PRE-SCHOOL PROGRAMS

The National Association for the Education of Young Children recommends parents interested in placing their children in pre-schools look for high-quality programs where:

• Teachers use a nationally recognized curriculum that fosters all areas of child development — cognitive, emotional, language, physical and social.

• There are no more than 10 children for every teacher.

• The school continually assesses a child's learning and development and shares those insights with parents.

• Teachers have bachelor's degrees.

• Parents are allowed to visit the program at any time.

• The school promotes the nutrition and health of children and protects staff and students from injury and illness.