In the national debate over what to do about the growing number of working people with little or no health insurance, no other company may be taking more heat than the country's largest employer, Wal-Mart Stores.

The company, despite its popularity with consumers, has grown accustomed to being accused of crushing Main Street merchants with its sprawling stores and low prices and of driving down wages for workers across the retail industry. And more than a million former and current female Wal-Mart employees are part of a sex discrimination lawsuit that the company is fighting.

Now, Wal-Mart finds itself under attack for what critics see as its miserly approach to employee health care, which they say is forcing too many of its workers and their families into state insurance programs or making them rely on charity care by hospitals.

Wal-Mart vigorously defends its health care policies, saying it offers affordable coverage for all employees.

The company says it has no way of knowing how many of its employees, whom it calls associates, or their families are insured under state programs. The larger issue of whether companies can and should absorb the soaring cost of health care is a national issue, said Susan Chambers, the executive vice president who oversees benefits at Wal-Mart. "You can't solve it for the 1.2 million associates if you can't solve it for the country.''

A survey by Georgia officials found that more than 10,000 children of Wal-Mart employees were in the state's health program for children at an annual cost of nearly $10 million to taxpayers. A North Carolina hospital found that 31 percent of 1,900 patients who described themselves as Wal-Mart employees were on Medicaid, while an additional 16 percent had no insurance at all.

And backers of a measure that will be on California's ballot tomorrow, which would force big employers like Wal-Mart to either provide affordable health insurance to their workers or pay into a state insurance pool, say Wal-Mart employees without company insurance are costing California's state health care programs an estimated $32 million a year.

Meanwhile, in Washington State, where the insurance commissioner is pushing the legislature to adopt a law similar to the one on the California ballot, companies that struggle to compete with Wal-Mart while insuring most of their own workers have become openly critical.

"Socially, we're engaged in a race to the bottom," said Craig Cole, the chief executive of Brown & Cole Stores, a supermarket chain that employs about 2,000 workers in Washington and adjoining states and pays for insurance coverage for about 95 percent of its employees. "Do we want to allow competition based on exploitation of the work force?" he asked.

Wal-Mart, which disputes the California figures and says it cannot verify the Georgia and North Carolina data, says its employees are largely insured. It cites internal surveys indicating that 90 percent of its employees have insurance - many through means other than Wal-Mart's coverage because they are senior citizens on Medicare, students covered by their parents' policies or employees with second jobs or working spouses.

"We are doing everything we can to take care of our associates and not shift costs," Ms. Chambers said.

The company has gone on its own offensive, saying last week that it was spending $500,000 to defeat the California measure, Proposition 72. The measure is opposed by many other businesses, particularly restaurants and retailers, and by Gov. Arnold Schwarzenegger, who asserts that it would impede the state's economic recovery and lead to a loss of jobs.

Wal-Mart has also been running a television ad nationally that features a Wal-Mart worker whose company health insurance covered his toddler son's treatments for life-threatening liver disease. "Without Wal-Mart,'' the father says, "I don't know that he would have made it."

But critics say the reality for too many Wal-Mart workers and their families is no insurance - either because they are unable to meet the company's eligibility requirements or because they cannot afford monthly premiums as high as $264 a month for family coverage on an $8-an-hour cashier's wage. Wal-Mart says its employees make $10 an hour on average.

Countering Wal-Mart's television ad, a California group supporting Proposition 72 has begun publicizing the case of a former Wal-Mart employee, Marco Guillen, who says he twice missed the company's annual enrollment deadline for health insurance. The first time, he said, was because he was confused about his eligibility. The second time, he said, was because he was in a coma after being in a car accident. His medical bills were about $1 million, he said, and were paid by the state's Medi-Cal version of Medicaid.

Wal-Mart declined to discuss the specifics of the case, saying that doing so would violate Mr. Guillen's rights under the federal laws governing patient privacy.

The company says it spent about $1.3 billion of its $256 billion in revenue last year on employee health care to insure about 537,000 people, or about 45 percent of its work force. Wal-Mart says that 23 percent of its employees are not eligible for coverage, but that it covers 58 percent of those who are.

That compares with an insured rate of 96 percent of eligible full-time or part-time employees of Costco Wholesale, the discount retailer that is Wal-Mart's closest competitor nationwide. Costco employees - most of whom are not represented by a union - become eligible for health insurance after three months working full time, or six months part time.

At Wal-Mart, which has no union employees, many who work full time must wait six months to become eligible. Part-time workers are not eligible for at least two years. Because of turnover, some employees never work long enough to become eligible.

If there is any place where Wal-Mart's labor costs find support, it is Wall Street, where Costco has taken a drubbing from analysts who say its labor costs are too high. Costco's pretax profit margin is only 2.7 percent of revenue, less than half Wal-Mart's margin of 5.5 percent.

Wal-Mart now asks employees to pay 33 percent of the company's cost of providing insurance, but says it plans to reduce that to 30 percent. So far, Costco has resisted pressure to increase employees' share of health care premiums beyond a planned target of 8 percent in 2007, reasoning that too many of their workers would be forced to drop coverage.

"From the very beginning of time, the founders here felt you have to pay a living wage and provide benefits," said Richard Galanti, the chief financial officer of Costco, which is based in Issaquah, Wash.

Wal-Mart finds itself up against a national tradition of providing health insurance to workers that took root during World War II, when wages were frozen and many companies offered health benefits in lieu of higher pay. After the war, unions at many big manufacturers also demanded generous benefits, and workers of all stripes throughout corporate America came to expect health insurance as a right of employment.

But in recent years, as global competition has become more intense, as organized labor has lost some of its clout and as medical costs have spiraled upward, employers have become increasingly unwilling to shoulder the cost of coverage. In 1987, only a quarter of the people working for large companies did not have insurance. By 2001, that figure had increased to about a third, according to a recent study by the Commonwealth Fund, a New York nonprofit group dedicated to health care research. Industry experts assume the percentage of working uninsured has continued to grow.

Other data indicate that of the 45 million people without health insurance in this country, nearly 70 percent are working full time or are the dependents of full-time workers.

Wal-Mart's rise to become the nation's biggest employer and largest retailer also speaks to a larger shift in the economy in the last generation, as a growing proportion of jobs shifted to service industries. Wal-Mart has succeeded because tens of millions of shoppers around the country flock to its stores for its sharply discounted prices. That business model, which is being widely imitated, depends on low-cost labor.

But government officials in various states, as well as some other employers, say Wal-Mart should nevertheless share more of the financial burden of its workers' health care.

"The Wal-Mart executives chose to remove the responsibility from themselves," said Mike Kreidler, the insurance commissioner for Washington State, who is pushing for a law requiring employers to provide insurance coverage either directly or indirectly.

Although Wal-Mart officials flatly deny it, some Wal-Mart employees say they are encouraged to turn to public health care assistance. When Wal-Mart hired Samantha Caizza, a single mother of three, as a cashier at its Chehalis, Wash., store last November, she says she was told by a personnel manager "to get ahold of the state" for coverage for her children.

Unlike many Wal-Mart workers, Ms. Caizza was willing to talk to a reporter about her experience because she was fired in June - for reasons she said had to do with union organizing activities. Wal-Mart said it could not comment on her case.

The company hands out instructions to its employees to help them to apply to social service agencies, which Wal-Mart says is simply part of the service they provide employees who need to have their income verified for any number of reasons.

Many employees say they simply cannot afford the health plans being offered. Ms. Caizza, for example, worked about 32 hours a week, making $8 an hour. Full-time employees make about $1,200 a month on those wages, meaning the $133 to $264 they are asked to pay for family coverage may not be within their reach. And even the cheapest plans come with a hefty out-of-pocket price for employees, where they may be on the hook for as much as $13,000 in medical costs for their families.

"While I was working there, I couldn't afford it for my children," said Beverly Winston, another former employee, who says she turned to state-subsidized coverage for her children while working at Wal-Mart in Renton, Wash., in the late 1990's. Ms. Winston is among the group of women around the nation now suing the company for sex discrimination.

"We work very hard for that to be affordable," said Ms. Chambers, the Wal-Mart executive, who said she thought the prices for the least expensive plans were "a very reasonable opening-price point.''

With the number of uninsured people in Washington climbing - now slightly more than a half-million people, or 9.4 percent of the population by one estimate - the state is grappling with the rising costs of caring for them. "The problem is getting much worse," said Mr. Kreidler, who says the cost of caring for the uninsured in Washington now approaches $400 million a year.

Asking the hospitals to keep paying the rising cost of the uninsured is not a solution, Mr. Kreidler said.

But Wal-Mart says it is not reasonable to ask companies like it to solve the problems of the uninsured and the escalating cost of medical care. It needs to be "part of a national debate," Ms. Chambers said.