The administration plan to give U.S. employes vouchers to cover the cost of no-frills health insurance policies could backfire and leave many people insufficiently protected if they are hit with major medical bills, according to a former chief actuary of the government health program.

Edwin C. Hustead, chief actuary of the Office of Personnel Management from 1972 to 1980, said the voucher plan (outlined here Thursday) looks good at first glance, but could "hurt federal employes in the long run."

OPM's plan, which has not been cleared by the White House, would eliminate the present system in which the government pays anywhere from 40 to 75 percent of an employe's health insurance premium, depending on the kind of plan the employe chooses.

Under the OPM plan, the personnel agency would no longer negotiate rates and benefits for plans in the federal health program. Instead, it would act as an overseer of the program and certify plans for participation.

The federal health plan now covers 10 million civil servants, members of their families and retirees--including about half the people in the Washington area.

OPM wants a system where employes and retirees each year would get a voucher to pay for health insurance. OPM says the vouchers would pay the full cost of premiums for low-option plans. Individuals who want the greater protection offered by so-called high-option plans would have to pay the premium difference.

Hustead, now a consultant with Hay Associates here, says the voucher plan presents a number of potential problems:

"If an employe with a family has, say, $75 a month to spend on health insurance we would certainly see a number of health plans suddenly spring up that offered apparently attractive benefits for exactly $75 a month. Each employe could then purchase coverage with no immediate out-of-pocket expenditure."

But, Hustead says, if the plans were no longer under OPM's control, "They would be free to offer any type of benefits that would appeal to the most healthy employes. For instance, most of the companies would offer dental care and not offer 'mental and nervous care.' The insurers would probably add many exclusions that are not allowed by OPM, such as exclusion of pre-existing medical conditions."

Non-covered items, Hustead warns, "would only be apparent after the claims were incurred. The initially attractive package could quickly turn sour, leaving the employe with uninsured bills."

If OPM got out of the contracting and auditing of insurance plans, Hustead said, companies could increase the percentage of premiums set aside for administrative expenses and profits. OPM nows limits them to no more than 10 percent.

Hustead also says that under the voucher plan, the government contribution might not keep pace with fast-rising health care costs. In the past two years the average premium paid by employes and the government has jumped 50 percent, but because of the percentage-sharing formula, the government contribution has remained relatively constant.

The voucher plan is now awaiting clearance from the Office of Management and Budget. That agency has insisted, and OPM has agreed, that if the voucher system is adopted, some plans be required to offer catastrophic coverage. But it is unlikely that any that do would offer them at rates that would be covered by the vouchers.

Once past the OMB, the voucher plan will be considered by a special White House cabinet council. If it buys the concept, and the president agrees, OPM will ask Congress to make the change. But many members of Congress--who are also covered by the federal health plan--have misgivings about the voucher system. So even if it goes to Congress, Democrats in the House would be expected to block it.