By ROBERT PEAR

ASHINGTON, Sept. 29 — The number of Americans without health insurance rose to 41.2 million last year, an increase of 1.4 million, and small businesses accounted for much of the erosion in coverage, the Census Bureau said today.

The proportion of the population without insurance also increased, to 14.6 percent in 2001, from 14.2 percent in 2000, the bureau said.

Lawmakers and lobbyists said the increase could propel health insurance back to the forefront of national political debate. But even as the need grows, the federal government and the states are less able to provide aid because their revenues have shrunk in the recession.

The proportion of Americans without insurance declined in 1999 and 2000, after rising relentlessly for a decade, even when the economy was booming.

Economists and health policy experts suggested several reasons for the latest increase in the uninsured: many people lost jobs last year, and employers are the primary source of health insurance for most Americans; rising health costs pushed up premiums, making insurance less affordable; employers passed on more of the costs to workers.

Households at every income level were more likely to be uninsured last year, the Census Bureau said. The change was particularly noticeable among people with moderate and high incomes.

The number of uninsured people with household incomes of $75,000 or more jumped to 6.6 million last year, an increase of 811,000 or 14 percent, from 2000.

Government health insurance programs covered more people last year, the bureau said. Medicaid, the federal-state program for the poor, covered 31.6 million people, up from 29.5 million in 2000, the bureau said.

Coverage appeared to deteriorate for adults, but not for children. The number of uninsured children, which declined in 1999 and 2000, was virtually unchanged last year, at 8.5 million. But the number of uninsured adults rose to 32.7 million, from 31.2 million in 2000.

The Census Bureau said that 11.7 percent of all children, 21.3 percent of poor children and 30.7 percent of all poor people were uninsured for the entire year in 2001.

Robert J. Mills, a statistician at the Census Bureau, said: "The percentage of people covered by employment-based health insurance dropped a point, to 62.6 percent in 2001. That was the principal cause of the overall decrease in health insurance coverage."

Small businesses are much less likely than larger companies to offer health insurance. At companies with fewer than 25 employees, the proportion of workers with health insurance declined last year, to 31.3 percent, but the Census Bureau detected no change at larger companies, where 66 percent of workers have coverage.

Still, employers of all sizes are passing on more of their health costs to workers and retirees.

Kate Sullivan, director of health policy at the United States Chamber of Commerce, said that many employers, while continuing to subsidize insurance for workers, had reduced subsidies for dependents.

"A lot of insurers are dropping out of the small-group market, and customers are balking at what they have to pay," Ms. Sullivan said. "A small employer with seven employees can easily spend $6,000 a month, nearly $1,000 per employee, for family coverage. Premiums are rising 20 percent a year."

Leslie M. Lauth, the owner of a microfilm and imaging company in Durango, Colo., said cost was "absolutely the major reason" she no longer provided health insurance for her four employees. Instead, Ms. Lauth said, she offers each worker $75 a month for insurance. But since the employee would also have to pay $75 to $100 a month, she said, the workers generally forgo coverage.

The number of children without insurance leveled off last year, after declining by 1 million in 1999 and by 700,000 in 2000.

"Progress stalled," said Genevieve M. Kenney, an economist at the Urban Institute here. "Kids seem to be holding their own, but they are not making further progress."

In 2001, the Census Bureau said, some children lost health insurance that they had been receiving from their parents' employers, but this decline was offset by an increase in coverage under Medicaid or the Children's Health Insurance Program.

The number of children with employer-sponsored health insurance dropped by 1 million last year, to 46.4 million from 47.4 million in 2000. At the same time, the number of children with government health insurance rose by nearly 1.2 million, to 18.8 million.

Many more children could be enrolled. "Half to three-fourths of all uninsured kids are eligible for Medicaid or the Children's Health Insurance Program," Ms. Kenney said. "In many cases, parents don't know their children could qualify."

States have not used all the money available to them under the Children's Health Insurance Program. When the new fiscal year begins on Tuesday, $1.2 billion of federal money will revert to the Treasury and can be used for other purposes unless Congress preserves it for child health care.

"It would be a huge mistake to let this money disappear," said Thomas A. Scully, administrator of the federal Centers for Medicare and Medicaid Services.