The Reagan administration has formally asked Congress to let the government give its active and retired workers vouchers every year to buy their own health insurance.

Currently the government pays 40 to 75 percent of the health insurance premiums for its employes and retirees. The giant health program covers 10 million people, including about half the population of metropolitan Washington.

The percent the government pays is based on a complicated calculation of the premium charged for the most expensive option of six major plans (there are about 130 in the program). The percentage the government pays also varies according to the actual cost of the policy the employe or retiree picks.

Under the voucher plan, submitted earlier this week by the Office of Personnel Management, workers and retirees would get a voucher (check) that OPM says would be sufficient to cover 100 percent of the premium for so-called low-option (no-frills) insurance plans.

Individuals who found plans that cost less than the amount of the voucher could pocket the difference, OPM says.

People who wanted more comprehensive and costly plans would pay the difference in premiums themselves out of regular payroll deductions.

In a letter to Congress, OPM Director Donald J. Devine said the proposed plan "embodies an exciting free-market method of providing health insurance" for federal workers that would give them "greater choice" and help the government hold down rising medical and hospital costs.

OPM said the vouchers, if Congress buys the idea, would be enough to pay the full premium of a low-option plan. The agency said such a plan would have to provide a "minimum level of catastrophic coverage," whatever that means.

Future increases in the amount of the voucher, OPM says, would be based on the rise in the "implicit price deflator" for the Gross National Product, an index that many economists feel is a better indicator of the cost of living than the more narrow Consumer Price Index.

Opponents of the voucher plan argue that it would lull employes into buying attractive-looking but inadequate insurance plans priced within the range of the voucher.

"Vouchers are fine if you never get sick and need health insurance," a congressional aide said. "But look out if you get stuck with a 'cheap' plan that doesn't cover you when you need it."

The House is in the midst of hearings on the much-criticized federal health program. Benefits have been cut about 12 percent in the past two years, while premiums for the average employe have risen by more than 50 percent.

Rep. Mary Rose Oakar (D-Ohio) and Sen. Ted Stevens (R-Alaska) have introduced bills that would raise the government contribution to health insurance premiums by 75 percent and 70 percent respectively.

Other members of Congress--anxious for a more direct way to control medical costs, which are rising about three times faster than the inflation rate--say the voucher system would put a break on price increased by encouraging workers to shop more carefully and give the government, which would control the size of the voucher, leverage on health carriers.

Even if Congress approved the voucher plan this year--and there is no indication that it will--it could not be put into effect until 1985 at the earliest.