Part of the 9.1 percent pay raise that most white collar federal workers are scheduled to receive next month will be eaten away by an average 15 percent icrease in health insurance premiums that will be imposed in January.

U.S. workers will pay $260 million more for health insurance in 1981 than they did this year. The government share of employe-family health insurance premiums will go up $375 million.

New rates and premiums in the federal employes health benefits program, which covers 10 million government employes, spouses and children, were announced yesterday by the Office of Personnel Management. OPM negotiates the insurance packages with more than 100 carriers in the program, which is the nation's largest.

Blue Cross-blue Shield, which covers five of every 10 people in the federal program, will introduce a dental benefits program in January. It will cover cleaning, filling or removing of teeth as well as routine examinations, placement of space maintainers and some categories of emergency treatment. Average out-of-pocket increase to employes in the Blues' plan will be 13.6 percent, or a biweekly increase in the family high-option plan from $26.87 today to $30.52 next year.

The total high option family plan premium for the Blues' program will go from $57.48 a month to $66.16. The government will pay $35.64 of the premium and the insured employe will pay $30.52.

Aetna, second largest carrier in the program, will not make any benefit changes for 1981. Its highest option family premium will rise from $43.17 a pay period to $50.75 every two weeks. Of that total premium, the government will pay $35.64 for high-option family coverage and the individual employe will pay $15.11 every two weeks.

Uncle Sam pays an average of 60 percent of the premium for health insurance for white and blue collar workers and annuitants. That average is based on the average rate of premiums charged by the six largest plans. In some cases the government can pay up to 75 percent of the individual rate.

Postal workers, whose unions bargain for them in pay and fringe benefit matters, typically have at least 75 percent of their health insurance premium paid by the U.S. Postal Service, which gets the money from people and businesses who buy stamps. Insome cases the USPS can actually pay up to 93 percent of premium, depending on the insurance plan.

In a program this large, statistics can be very confusing. The increase in premiums next year will average around 15 percent, within a rate rise range varying from 10 percent to more than 22 percent . One California carrier will raise biweekly employe premiums more than $20. A few, like the National Association of Postmasters plan, will reduce premiums. The Columbia (Md.) Medical Plan and Group Health Association will reduce premiums for low-option coverage, and make only modest increases in other options.

Many of the union-backed plans are open to nonmembers who pay a modest fee to join them. The majority of federal workers elect either the self-only or family high-option plans, which cost more than low-option plans with more limited benefits.

To make it easier for people to decide among the bewildering array of benefits, options and charges for the 121 individual plans, Office of Personnel Management will publish a benefit comparison chart of the larger plans that will be available for study at agency health and personnel offices.

Workers will have an "open season" period -- between Nov. 10 and Dec. 5 -- to make changes in their coverage if they so desire.