Political Washington, D.C., was understandably fixated on the outcome of the June 6 congressional race in San Diego as a harbinger for November’s elections. But the defeat of California’s Proposition 82 could end up being more important for the country’s future.

Proposition 82 would have committed America’s largest state to provide preschool education for all its 4-year-olds. It was rejected by a margin of 61 percent to 39 percent.

That’s important because a mounting body of academic evidence shows that investment in quality early childhood education would be America’s surest way of closing a growing opportunity gap between its social classes —a gap likely to grow wider as the globalized economy places ever-greater emphasis on high skills.

After reviewing numerous studies for the book “Opportunity in America,” to be published in September with Princeton University, Brookings Institution scholar Isabel Sawhill told me this week that “the place where you’re likely to get the biggest bang for the buck is making investments in children from less-advantaged families.”

She explained, “They start out way behind even before they enter school and they stay there. These gaps persist through the school years. If you don’t deal with them before they enter school, you’re stuck with a very stratified society.”

Two long articles last week in The Wall Street Journal and The Economist showed that the U.S. poverty rate, 10.5 percent, is the same as it was in 1979 (after dipping to 9 percent in 1999) and that the median wage of American workers has risen by less than 1 percent since 2001, despite roaring productivity gains.

Congressional Democrats last week released a domestic policy agenda that called for closing income and opportunity gaps much later in life than early childhood —by making college more affordable and increasing the minimum wage for workers.

Last month, the Bush administration proudly claimed that its tax-cut policies were cutting income inequality because the top 5 percent earned only 15.4 percent of the nation’s after-tax income in 2003, down from 19 percent in 2000, while the bottom 20 percent increased its share from 2.3 percent to 2.5 percent.

As The Washington Post noted, however, Treasury Department data also showed that the 2003 income gap was still larger than it was in 1990, when the top 5 percent took home 12.9 percent of the nation’s income.

And Census Bureau data shows that median household income for the top 20 percent of families was 14 times that for the bottom 20 percent in 2000. By 2004, it was 14.8 times higher, suggesting growing inequality.

Another approach to closing the opportunity gap is that of the Bill and Melinda Gates Foundation, which is trying to end what’s been described as a “silent epidemic” of high drop-out rates from high school — about 30 percent of all students, and nearly 50 percent for blacks and Hispanics.

According to the current issue of Education Week, Gates-funded research shows that dropouts earn 34 percent less than graduates and 132 percent less than college graduates do and are four times more likely than college graduates to be unemployed, on welfare and to serve time in prison.

The Gates foundation has devoted $2 billion to improving U.S. education so far and has embarked on a program to infuse a new “three Rs” into high school —rigor, relevance and mentor relationships — to improve graduation rates and prepare graduates for college and skilled jobs.

Of course, those sums are dwarfed by the $530 billion that the United States spends per year on elementary and secondary education, including $13 billion in federal funds to help poor children.

But, according to Sawhill, “Education at every level tends to perpetuate rather than compensate for existing inequalities.

“We like to think of ourselves as a land of opportunity where all you need to do is work hard and play by the rules. And we don’t like to talk about class in the United States,” she said, “but you really do need to pick your parents well. Who your parents are has a very large effect on where you end up in life as an adult.”

Besides giving children their genes, well-off parents give them good preschool preparation, a bigger property tax base for their public schools and, on average, much better chances for admission to quality higher education.

U.S. community colleges create opportunities, but Sawhill said the research shows that quality early childhood education — better than what’s now available in the federal Head Start program — would pay the biggest dividends.

Which is why the failure of Proposition 82 is so dispiriting. Granted, it probably was overambitious, providing universal preschool rather than being targeted to the poor. And it was complicated by allegations of misuse of public funds by its chief promoter, movie director Rob Reiner.

Nationally, 65 percent of parents with college degrees enroll their children in preschool, compared with 34 percent for those who didn’t graduate from high school, and 50 percent who did.

To make America really a land of opportunity, both parties should put it on their agenda to start educating kids at age 3.