Democratic gubernatorial candidate Timothy M. Kaine vowed Tuesday to make preschool available to every Virginia 4-year-old, a costly but potentially popular promise three months before Election Day.

At a town meeting at a suburban Richmond elementary school, Kaine said that as governor he would implement Start Strong, a $300 million-a-year program to guarantee a year of school before kindergarten to all children whose parents choose to enroll them.

"Ninety-five percent of a child's brain growth is complete by age 5," Kaine told teachers and others at the meeting. "It's time we recognize that we have to invest dollars and invest them earlier if we want our kids to succeed."

The idea would dramatically increase the access in Virginia to early childhood education. Kaine's plan would pay for preschool without regard to a parent's income.

Research has shown that high-quality preschool can boost learning, especially for poor children, by preparing children for school. But it's also costly: Kaine estimates it at $5,400 a student. A similar program in Florida was approved by a voter initiative and begins this school year, but spending on it has been scaled back by the legislature.

A spokesman for Kaine's Republican opponent, former attorney general Jerry W. Kilgore, called the idea "laudable" but said it is not in Kilgore's platform for education reform. Press secretary Tim Murtaugh questioned whether Kaine could make the program work.

Sen. H. Russell Potts Jr. (R-Winchester), who is running for governor as an independent, declined to comment, saying he needed more information.

Access to preschool varies widely in Virginia. About 24,000 of the state's 100,000 4-year-olds attend publicly funded preschool.

Very poor children, whose parents' incomes meet the federal definition of poverty, can qualify for Head Start programs. Some school systems offer their own pre-kindergarten classes for some of their students. And many parents pay for private preschool.

In growing Loudoun County, where taxpayers already provide pre-kindergarten education for at-risk students who do not qualify for federally funded Head Start, School Superintendent Edgar B. Hatrick III said a plan to provide universal pre-kindergarten education would require new classrooms.

"As I understand it, as fast as anyone can build preschools here, they're filled and have waiting lists," he said. "That's churches, cooperative parents groups, actual private schools, our Head Start [and local program], that's all combined. There would be capital implications to this."

Still, Hatrick, who is immediate past president of the Virginia Association of School Superintendents, said he is sympathetic to the goal. "What we know about educating children is the earlier we get them, the easier it is to educate them," he said.

Maryland does not offer pre-kindergarten to all children but is developing a state program to offer it to some low-income students.

Kaine's proposal would provide the money for school systems to expand their programs to guarantee that any parents who wanted to enroll their children in preschool would have that opportunity.

He said the state would earmark $74 million a year for each of the four years he serves as governor to meet that goal. Most of that money would come from savings the state would get from spending less on remedial education, he said.

If elected, he said, he would set up local councils in each jurisdiction to decide how to provide the preschool. In some cases, that could be at a public school. In places such as Loudoun, where school buildings are crowded and construction is expensive, it could be through a network of existing private preschools, Kaine said at yesterday's meeting.

Education advocates generally praised Kaine's proposal, saying that too many children enter the nation's public schools unprepared for the challenges they will face.

But they also said the desire to provide money for everyone, while good in theory, often means that not enough money would get to the children who need help the most.

"If I was in an ideal world with endless resources, I'd say, yeah, bring it on," said Amy Wilkins, a principal partner at the Education Trust, a nonprofit research organization. "We don't live in an ideal world. We live in a world of relatively scarce educational resources. If the research says that low-income kids are furthest behind, then you have got to set priorities."

Wilkins also said research proves that only high-quality preschool provides lasting benefits to students as they move through later school years. That means providing small classes and experienced preschool instructors who have college degrees.

"Something that is slapped together doesn't get it," she said, noting that Florida's soon-to-start program might be stretched too thin to have a real impact on learning. "To cover all kids, the program quality is not going to be very good."

The cost of Kaine's proposal emerged as a key point of contention between the candidates Tuesday as Kaine attempted to explain how the state could afford it.

Kaine said the state would save some money on remedial and other education programs that would no longer be necessary. But even before Kaine's announcement, Kilgore's campaign had sent out an e-mail calling Kaine a "tax and spend liberal" and detailing "billions" in spending he has proposed.

Kaine's campaign, which has accused Kilgore of proposing spending without saying how he will pay for it, responded quickly with an e-mail titled, "Pot, meet Kettle."

Staff writer Rosalind S. Helderman contributed to this report.

Loudoun County Superintendent Edgar B. Hatrick III says early education is valuable for children.