Nearly 1 in 4 Californians under age 65 had no health insurance last year, according to a new report, as soaring unemployment propelled vast numbers of once-covered workers into the ranks of the uninsured.

The state’s uninsured population jumped to 8.2 million in 2009, up from 6.4 million in 2007, marking the highest number over the last decade, investigators from UCLA’s Center for Health Policy Research said.

People who were uninsured for part or all of 2009 accounted for 24.3% of California’s population under age 65 -- a dramatic increase from 2007 driven largely by Californians who lost employer-sponsored health insurance, particularly over the last year.

Among those over age 18, nearly 1 in 3 had no insurance for all or part of 2009, the UCLA researchers found. The ranks of uninsured children also grew. The study was based on phone interviews from 2007, updated with current insurance enrollment data.

Adults over age 65, who are covered by the federal Medicare insurance program, were not included.

As a result of the insurance gap, many already strapped Californians have put off needed medical care and usually wound up crowding emergency rooms, receiving costly care on the run. Hospitals and insurance companies often pass on those expenses to customers with insurance, increasing the cost of healthcare and driving up rates for those who have coverage.

The new UCLA estimates arrive as President Obama and congressional Democrats scramble this week to finalize an agreement on healthcare reform. Democrats who are pressing the overhaul say it would expand health insurance to tens of millions of uninsured people across the country.

Yet even as leaders in Washington seek to expand coverage, California officials are wrestling with budget proposals by Gov. Arnold Schwarzenegger to cut or eliminate publicly funded insurance programs that critics say cover more than 2.5 million low-income children and their parents -- some of whom lost coverage because of layoffs.

California has one of the highest uninsured rates in the country, alongside Texas and other states with high unemployment. Because California’s population is so large, however, it has more uninsured people than any other state.

The number of uninsured has swelled in tandem with California’s unemployment rate, which rose to 12.3% in December from 5.7% two years earlier, and as employers shifted more healthcare costs to employees.

Bruce Kuhlmann of Santa Rosa was laid off in December 2008 from his job as a technology sales executive in Northern California. He has depleted much of his retirement savings to pay for care since he was diagnosed with cancer last month.

The father of three, including two college-age children, has found it difficult to buy insurance on the individual market.

Kuhlmann, 58, worries about affording an operation that he believes will cost about $30,000.

“I’ve spent a fortune of my own money,” Kuhlmann said in a phone interview as he prepared to undergo a medical procedure at Santa Rosa Memorial Hospital. “I have a house mortgage. It’s hard to get a job because I don’t feel so good. Everything is negative.”

UCLA researchers said they were surprised by the big jump in the uninsured population from 2007 to 2009. The director of the health policy center, E. Richard Brown, said the state’s 8.2 million people without coverage was the highest number he had seen in nearly three decades of studying the issue.

“California’s situation is pretty dire with respect to healthcare coverage,” Brown said.

The numbers of uninsured are likely to climb as the state’s jobless rate is expected to remain in the double digits well into next year.

“The shocking increase in people losing insurance spotlights the problem that . . . coverage may not be there for us when we need it,” said Anthony Wright, executive director of Health Access California, a Sacramento consumer group. “This adds more urgency to the debate over the pending health reform proposals, which directly address the insecurity Californians are facing.”

Researchers said federal subsidies for laid-off workers helped some people who lost jobs and coverage. Yet even so the loss of insurance affected young and old alike.

The percentage of uninsured children grew to 13.4% in 2009 from 10.2% in 2007. The increase would have been greater if not for insurance programs paid for by the state and federal governments. The number of uninsured children rose from 1.1 million to 1.5 million over the two years.

The study’s lead author said that adults who lack the safety net face the most daunting prospects.

“Being uninsured has real human consequences. . . . It is costly for all of us,” said Shana Alex Lavarreda, director of health insurance studies at the UCLA research center. “It makes reforms of the system absolutely essential.”

duke.helfand@latimes.com