The Washington area's 90,000 retired federal, postal and military retirees will get a tangible, spendable reminder of inflation this week: Annuity checks reflecting a cost-of-living (COL) adjustment that will boost retirement income here more than $13 million a month.

For the typical retiree the 6 percent (before taxes) adjustment will translate into about $48 each month. Retirees are due another COL raise this October. But President Carter and Congress are proposing to end the six-month COL adjustments. They would limit federal and military retirees to a single adjustment each year -- either in June or July.

The 6 percent raise for retirees was effective in March, but will first show up in checks mailed for delivery this week. Retirees got a 6.9 percent adjustment effective last September (payable first in October checks). They are due another increase of at least 3.8 percent this fall.

President Carter yesterday formally endorsed actions of the House Budget Committee that would eliminate the March and September federal-military COL adjustments.Under the plan retirees would get an "interim" COL increase this July in place of the September 1980 and March 1981 raises due them. After the July increase, they would get raises each June or July.

(There is a group in government arguing against any "interim" payment for annuitants this year.The primary argument is that skipping further raises this year would save Uncle Sam at least $200 million.)

Opponents of the two annual COL raises argue that social security recipients are limited to a single adjustment each year, and that eliminating one of the two federal-military raises would save the government millions of dollars in compounding.

Federal retirees say Congress promised them the COL adjustments every six months in return for earlier benefits cutbacks, and that the payments follow inflation rather than cause it. Be that as it may, Congress and the White House appear to be in the mood to eliminate one of the two annual federal raises. Government officials say the 6 percent boost nationwide will increase the value of federal pensions $66.3 million per month.