Under the federal law, consumers who have previously been rejected for private insurance because of a pre-existing condition will be able to enroll, and those who cannot afford to buy their own insurance can receive government-subsidized premiums.
"I think it's hard to overstate how big a change this is: People will no longer pay based on how sick they are, but on what they can afford based on a percentage of income.
That's a transformational change in the way health care works," said Anthony Wright, executive director of Health Access California, which has advocated for greater health care coverage for the poor.
The Affordable Care Act, also known as "Obamacare," will dramatically change the way many Americans will get health insurance and marks the most extensive change to the nation's health care system since Medicare and Medicaid became law in 1965.
California is being seen as a laboratory for the health care overhaul, and call center workers have been training for months to answer questions. The three call centers — in the eastern San Francisco Bay Area city of Concord, Fresno and the Sacramento suburb of Rancho Cordova — already have been flooded with calls.
Latinos, who make up nearly half of the 5.3 million uninsured Californians who are eligible to apply, have been expressing particular interest, said Santiago Lucero, a spokesman for Covered California, the name of the health exchange. Information is available in 13 languages, but those who are in the country illegally are not eligible for coverage.
Despite the significance of Tuesday's opening, officials do not expect a wave of applications immediately because comparing the available plans and filling out the application will be time-consuming.
"There are four different levels of health plans, and then within each level there are 12 different companies," to choose from, Lucero said. "They have to pick which would best fit their financial and health needs. ... It may take some time before they make a decision."
Beginning in 2014, virtually all Americans will be required to have health insurance or pay an annual penalty to the government. The penalty for an individual starts at $95 in 2014 but rises to a minimum of $695 by 2016.
Californians who have health coverage through an employer will be largely unaffected by Tuesday's opening of the exchange, which is primarily for the poor, low-income earners, and individuals and families who already buy their own health insurance.
Actual coverage through insurance purchased on the exchanges will start Jan. 1.
California is expected to receive about $300 million in federal money for outreach and advertising, some of which is going to a wide array of groups trying to promote the health exchange, but surveys show that many people remain confused about the law and how it will affect them.
Covered California officials are holding events throughout the state Tuesday to promote the opening of the exchange. Glitches are possible, especially if too many people try to access the website, www.coveredca.com.