They've been dubbed the "young invincibles," people in their 20s and 30s who must sign up for medical insurance in droves to ensure the success of the new health care law.

But a new California poll indicates that perhaps they should be called the "young convincibles."

The startling finding by the Public Policy Institute of California says that young and healthy people are overwhelmingly more likely to seek health insurance than older and sicker people.

Some health care experts said the poll released Wednesday is extremely good news for Obama administration officials who have been in a bunker defending the health care law after its shaky October rollout. The encouraging poll numbers are key because younger people would help subsidize the cost of insuring older and sicker people -- and keep rates on the state's new online health insurance marketplace affordable.

Many health care economists have worried that young people, convinced they don't need health insurance, would opt to pay a minimum $95 penalty -- thus undermining the new law.

The poll finding "runs counters to what a lot of people were expecting," said Gerald Kominski, a UCLA health care economics professor who believes that what's persuading young people to plan on signing up is the significant subsidies many will get from Uncle Sam. If those young people follow through on their intentions, he said, it would result in keeping the cost of the new exchange health plans low.

"Not every young person will qualify," he said, "but many will -- and that will make it easier for them to obtain insurance."

California, the nation's most populous state with the greatest number of new health care enrollees, is considered a bellwether for the ultimate success of the Affordable Care Act, commonly known as Obamacare.

The PPIC surveyed 1,701 California adults from Nov. 12 to Nov. 19. The overall margin of error of the poll was plus or minus 3.6 percentage points -- 8.8 points for the subgroup of 242 uninsured residents.

The poll showed that 72 percent of uninsured residents ages 18 to 44 say they are more likely to seek health insurance. Of those age 45 or older who lack health insurance, 51 percent told pollsters they planned on getting it.

The PPIC numbers on young people who plan on signing up for insurance appear to mimic an early analysis by Covered California, the state's online health exchange, that trumpeted its first-month enrollment figure of 30,830 people, including 6,900 who are between 18 and 34.

But some experts say the jury on the health care law is still out because they need to see how many younger people actually carry through on their intention to sign up.

"Reading these numbers, they appear flipped," said Glenn Melnick, a health care economics professor at the University of Southern California. "So the question is: 'Why?' "

Why, for instance, are people 45 and older not as inclined to buy an insurance policy?

"As people get older, they use more services," Melnick said. "You expect this group to be a little more responsible, planning their health insurance and having done some research. Maybe they found they could not afford it and the cost of premiums have gone up" because of the new law.

Kominski said that could very well be a reason.

Through the Covered California exchange, for example, a 28-year-old San Jose resident with an annual adjusted gross income of $25,000 would find that the lowest price PPO plan charges $216 a month. But this person would be eligible for a $148 subsidy and thus pay only $68 monthly.

By contrast, a 52-year-old San Jose resident with a $50,000 annual adjusted gross income would not qualify for a subsidy. So the cheapest plan would cost him or her $388 a month.

Kominski said many people in their late 40s and 50s still think of themselves as healthy and might resist the higher premiums charged by insurers. Under the health law, the cost of policies can be three times higher than those for young people. And because older people tend to make more money, many will not be eligible for the federal subsidies.

Moreover, he said, the attitude of many young invincibles that they won't get sick "is not exclusive to young people."

The PPIC poll also showed that Californians are divided in their assessment of the health care law. Forty-four percent view the law favorably, compared with 44 percent unfavorably.

That contrasts with a nationwide Kaiser Family Foundation poll that showed 33 percent of Americans viewed the law positively, compared with 49 percent who had an unfavorable opinion.

Mark Baldassare, president and CEO of the PPIC, said the poll reflects only the very early stage of how a major public policy is being received by Californians.

But, he said, "we're seeing a solid majority reflecting awareness as well as interest. The degree to which they follow through (on signing up for insurance) will be something we will want to look at after a few months."

Contact Tracy Seipel at 408-920-5343. Follow her at Twitter.com/taseipel.