Of the millions of Americans without health insurance, a surprising 20 percent are eligible for an employer plan.

That's a far higher percentage than anyone imagined, says Peter Cunningham, senior health researcher for the nonpartisan Center for Studying Health System Change (CSHSC) in Washington, which has just released a new study of the uninsured.

Why do some breadwinners leave themselves and their families unprotected? Most of the time there's one simple reason: They can't afford the policy's price. They have coverage at their fingertips, but family incomes are too low to take it up.

Americans with livable incomes don't realize how often the poor pay higher prices than anyone else for many products and services. The CSHSC study shows that that applies to health insurance, too.

At firms paying lower wages (typically, smaller firms), employers pay less toward the cost of family plans.

For example, take the cheapest family policy. It costs workers an average of just $84 a month, at companies where the typical wage exceeds $15 an hour, CSHSC reports. That compares with a big $130 a month in firms where hourly wages fall below $7.

For lower-income families, that's a double whammy. First, they pay 55 percent more for family insurance than higher-income families do. Second, the cost of the premiums eats up a higher percentage of their incomes. No wonder they have to say no.

Smaller companies are also suffering larger increases in their health insurance costs, according to a health benefits survey released this week by the Kaiser Family Foundation and Health Research and Educational Trust.

Premiums for employer-sponsored plans rose an average of 4.8 percent in the 12 months ending in spring 1999. For the smallest firms, premiums rose 9.2 percent. That's a recipe for forcing even more people out of the health-insurance system.

CSHSC's findings suggest a direct way of reducing the number of uninsured: Find ways of lowering the price that employees pay, especially for family plans, so that more people can afford them.

Enrolling more workers in existing company plans would be of more help than any of the insurance plans Congress passed or proposed in recent years, Cunningham says.

Congress and some of the presidential candidates have various ideas for helping with premium costs. None of them focus specifically on people who can't afford their company plans, but many of them would still be helped. For example:

* Presidential candidate Bill Bradley would subsidize health insurance for people with low to moderate incomes. They'd get help on a sliding scale, with the poorest receiving enough to cover a policy's full price.

Bradley would start by requiring that all children be insured through federally approved plans (although he doesn't propose a way of enforcing that rule).

Next, he'd institute similar subsidies for the adults who chose to join. They could buy employee coverage, individual coverage or join the health plan used by all federal workers (including Congress).

There are two risks to such a plan.

First, some small companies might drop the health insurance they currently offer and dump their workers into the federal pool. If they did so, however, they'd be wiping out health benefits for their higher-paid workers, too. They might not want to do that.

* Second, some workers who carry company insurance might find it cheaper to scoot to the federal plan. Businesses would get a break, but the government's costs would rise even more.

The big question is whether the industry and the taxpayers actually want to do this much for the uninsured.

* Vice President Gore would let states expand the subsidized Children's Health Insurance Program (CHIP).

Right now, CHIP is only for the children of the very poor. Gore would extend it to children from moderate-income families, and push the states to sign up more people. The uninsured parents of children eligible for CHIP and Medicaid could get into the program, too.

But why discriminate against uninsured workers who happen not to have children? This helps some workers while leaving out others with the same modest incomes.

* The health-care bill recently passed by the House of Representatives would allow small businesses and associations to band together in new buying pools. They'd be encouraged to set up bare-bones policies. The insurance would cost less because it would cover fewer medical bills. In past experiments, however, bare-bones policies haven't been very popular.

At best, all these are partial solutions, Cunningham says. Something is better than nothing, but the problem doesn't go away.