Preschool is having its moment, as a favored cause for politicians and interest groups who ordinarily have trouble agreeing on the time of day. President Barack Obama devoted part of his State of the Union address to it, while the deeply red states of Oklahoma and Georgia are being hailed as national models of preschool access and quality, with other states and cities also forging ahead on their own.

Enrollment in state-funded preschool has more than doubled since 2002, to about 30 percent of all 4-year-olds nationwide, and much more growth is expected. In just the past year, Alabama, Michigan, Minnesota, Montana and the city of San Antonio have enacted new or expanded programs, while in dozens of other places, mayors, governors and legislators are making a serious push for preschool. In New York City, where new Mayor Bill de Blasio was elected on a promise of universal prekindergarten, the dispute between him and Gov. Andrew M. Cuomo is not over whether to expand the program, but how.

For generations, it was largely Democrats who called for government-funded preschool — and then only in fits and starts — and that remains the case in Congress, where proposals have yet to gain traction among Republicans. But outside Washington, it has become a bipartisan cause, uniting business groups and labor unions, with Republican governors like Rick Snyder of Michigan and Robert Bentley of Alabama pushing some of the biggest increases in preschool spending.

They point to a growing body of research on the effectiveness of early intervention and the importance of early child development.

"It’s a human need and an economic need," said Snyder, who raised preschool spending $65 million last year and will propose a similar increase this year, doubling the size of the state program in two years. He called the spending an investment whose dividends "will show up for decades to come."

Analysts also see politics behind the shift at the state level, with preschool appealing particularly to women and minorities, groups whose votes are needed by Republicans.

"If you cast it as an issue of inequality, Republicans get their back up right away, but there’s a sincere and growing concern on the part of a lot of Republicans about how to increase economic opportunity," said Ron Haskins, co-director of the Center on Children and Families at the Brookings Institution and a former policy adviser to President George W. Bush. "And politically, they also really want to change their image as the party that just says no, to find something with broad appeal that they can say yes to."

Few government programs have broader appeal than preschool. A telephone poll conducted in July for the First Five Years Fund, a nonprofit group that advocates early education programs, found that 60 percent of registered Republicans and 84 percent of Democrats supported a proposal to expand public preschool by raising the federal tobacco tax.

"Preschool is, generally speaking, a crowd pleaser," said Chester E. Finn Jr., president of the Thomas B. Fordham Institute, a conservative-leaning education policy group.

Business and law enforcement groups, which have the ear of conservative lawmakers, have taken the lead in lobbying for preschool, arguing that the economy requires an educated workforce and that starting early is cheaper, more efficient and will mean fewer children turn to crime in later life. A group of police chiefs and prosecutors recently issued a report in support of preschool titled "I’m the Guy You Pay Later." Business leaders argue that the benefits are not just long-term, but immediate — that preschool creates jobs, leaves low-income parents free to work and reduces the number of children in high-priced special education programs and those having to repeat grades.

"That’s a part of the argument that we’ve only started to develop, but I think it’s very persuasive," said John E. Pepper Jr., a former chairman and chief executive of Procter & Gamble, and one of the leaders of ReadyNation, a national group of business leaders pushing for preschool expansion.

Though Republicans and Democrats are clashing with teachers unions over teacher evaluations and standardized testing, those unions strongly support preschool expansion if it means more jobs in public schools.

Not that any of these factors will necessarily change things in Congress, where Republicans have steadfastly opposed the proposal by Obama, who has called for a $75 billion federal investment in preschool over 10 years, paid for with an increased tobacco tax.

Preschool advocates say that Sen. Lamar Alexander of Tennessee is one of the Republicans most receptive to their arguments, but he rejected the president’s plan as a top-down mandate from Washington. "Early childhood education is important and we should try to make it available to the largest number of children possible," he said in an email. "But most of that should be done by local communities and state governments."

Sen. Tom Harkin, D-Iowa, has introduced a prekindergarten bill that would cost $34 billion over five years. In a nod to conservative resistance to a tobacco tax, Harkin has said he is open to any funding mechanism, but he has found no Republican co-sponsors.

"There’s still that ideological barrier that Republicans have that the federal government has no business being in elementary and secondary education," he said.

Haskins, of Brookings, said congressional Republicans oppose a federal program "first because it’s an Obama initiative and you may have noticed that they aren’t in love with the guy," and because of a general resistance to new social programs and taxes. He and other analysts said Republican governors tend to take a more pragmatic, less ideological approach to issues than their congressional counterparts, and have less fear of Tea Party-inspired primary challenges.

Critics say public funding of early education has been ineffective, pointing to studies that show the academic effects of Head Start — the most widely-known federal preschool program — have faded by third grade. Andrew J. Coulson, director of the Center for Educational Freedom at the Cato Institute, a right-leaning think tank, said studies that have demonstrated long-term benefits of preschool, such as higher graduation rates, fewer behavioral problems throughout elementary and high school, and reduced crime rates, were conducted on small populations of children enrolled in costly programs.

But researchers say the quality of Head Start programs vary widely, and that studies often compare Head Start participants with children in other, potentially better, preschool programs. James J. Heckman, the Nobel Prize winner and University of Chicago economist whose study of the economic benefits of the Perry preschool program in Michigan in the 1960s is often cited by advocates, said good quality does not require an exorbitant price tag. "If we pare it down to its essentials," Heckman said, "it may not be very expensive."

Advances in the sciences also point to the importance of the earliest years. "There’s overwhelming and indisputable evidence across the entire biological sciences that early experiences shape the developing brain," said Jack P. Shonkoff, director of the Center on the Developing Child at Harvard University.

Even those who agree that early education can reap long-term benefits say policymakers should not bank on miracles. Mark Lipsey, a psychologist at Vanderbilt University who is leading a study of a voluntary preschool program in Tennessee that has shown early indications of some lasting social benefits for children who participate, said advocates sometimes made preschool sound "like you put them in the pre-K washing machine and scrub them clean and they come out after that."

"But effects of poverty and disadvantaged environments don’t work that way," Lipsey said. "It’s a cumulative process and it’s going to take cumulative efforts to make a big difference. There’s potential here but we also have to be realistic."

There are almost as many ideas about how to pay for preschool as there are programs. Several governors have advocated finding the money within existing budgets. San Antonio adopted a sales tax increase, while Virginia uses lottery money for its program. De Blasio wants to increase income taxes on New York City’s wealthiest residents, and Maine lawmakers are seeking to use casino revenue. One legislator in Maryland has proposed legalizing and taxing marijuana to finance preschool.

In a 2012 review by the National Institute for Early Education Research at Rutgers University, three conservative states, Oklahoma, Georgia and West Virginia, stood among the leaders in the number of children enrolled in publicly financed preschool and in the quality benchmarks they met. Florida had the highest enrollment in 2012 – almost four-fifths of all 4-year-olds – but with about 84 percent of those children attending classes run by private, faith-based or family centers, the state’s preschool programs did not fare well on quality measures. Other states with more than 50 percent enrollment included Wisconsin, Iowa, Texas, and just one strongly liberal state, Vermont.

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Richard Pirez-Peqa and Motoko Rich, New York Times

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