Metropolitan Washington's 100,000 retired federal, postal and military people are due a cost-of-living raise in March that could top 10 percent.

Retirees get a full-year COL catch-up raise that goes into effect in each March. It is reflected in monthly checks mailed out in April. The 1982 raise will match the rise in living costs from January to December of this year as measured by the Consumer Price Index. Based on the October CPI, retirees are due at least 8.1 percent. That will be adjusted upward based on the CPI figure for November and December.

According to the Office of Personnel Management the average federal retiree gets a monthly annuity of $958. The average survivor benefit is $436 per month. The monthly payment to civilian retirees or their survivors currently is $1.3 billion. Unlike Social Security benefits, which are tax-free, federal annuities are subject to taxes.

Retirees used to get COL catch-up raises every six months -- in March and September. But last year Congress and the White House changed the system, despite a campaign pledge by President Reagan not to tamper with the frequency of COL raises. Many people think that retiree resentment over the COL flip-flop hurt Republican candidates in the November election in Virginia, which has big concentrations of federal employes, military personnel and retirees in the Washington suburbs and in the Tidewater region.