About $7 billion is at stake. More than 1 million federal and postal workers must figure out by January what to do with money in their tax-deferred thrift savings plan accounts, which are an optional part of the pension program.

High-income workers in the new Federal Employees Retirement System pension plan could have as much as $60,000 in their individual accounts, thanks to earnings and partially matching government contributions. Employees under the old Civil Service Retirement System pension plan have smaller accounts because they can't contribute as much or get a government match.

Most of the money invested by workers, and all government contributions, have gone into the G-fund, made up of special treasury securities. But next year all investment restrictions are lifted. That will let workers invest in any of the savings plan's options.

Workers have until January to decide what to do with money in their accounts and future allocations they will make via payroll deduction. Among the choices:Stick with the super-safe G-Fund (treasury), which is being invested at 8.625 percent this month. Put some or all investments into the higher-risk C-fund (stock market option) or F-fund (bond market option). Go for the brass ring: Transfer all money in the G-fund account to stocks or bonds. Money invested that way will be put into the option of the employee's choice at the closing prices of the Standard & Poor's 500 index (for stocks) or Shearson Lehman Bros. aggregate bond index as of Jan. 31, 1991. Use the more cautious dollar-cost averaging approach. Gradually invest in the C or F funds over a longer period. Investing without regard for the market value of stocks or bonds, many analysts say, tends to produce an average purchase price rather than highs and lows. Example:

An employee with $5,000 in the treasury fund wants a balanced portfolio that is 50 percent stocks, 30 percent government securities and 20 percent bonds. The employee transfers $2,500 to the stock fund and $1,000 to the bond fund via interfund transfers, which will be effective Jan. 31.

The purchase price of the C and F fund investments would depend solely on the value of those indexes on Jan. 31. If the employee wants to spread the risk, future payroll contributions could be directed to the C and F funds until the desired ratio is achieved.

Payroll withholding contributions illustrate the dollar-cost averaging concept. Employees allocate money each pay period and the investments occur at closing stock or bond index prices on the day of investment. That is four times a month for the stock fund and twice a month for the bond fund.

Under current investment rules, the G-fund (treasury) is worth $7 billion. Last month the stock fund was worth $156 million and the bond fund was worth $48 million. Because investment restrictions are being lifted next year, federal officials expect hundreds of thousands of employees to change their investment options -- or sign up for the plan -- this open season.