Bad news for President Carter and for budget-cutting members of Congress:

Over the past 30 days this column has averaged more than 1,200 letters a day, every day. They are mostly from civil servants and retirees, and mostly on a single subject: Don't mess with our retirement future! Don't try to cut our cost-of-living raises because costs are high!

The outpouring of mail -- over 38,000 letters and cards between April 13 and May 13 -- is the equivalent of a message from one of every nine government employes in the metropolitan area.

The letters and cards were in response to an April 13 column. It asked federal workers how they felt about congressional -- White House plans to cut back their cost-of-living raises, and future plans to force federal and postal workers to come under social security. It also asked what they would do -- at the ballot box -- to politicans who support either or both. t

(Both the Senate and House have already approved budget resolutions that would eliminate the cost-of-living adjustments retirees get every six months. Instead of March and September inflation-catch-ups for U.S. civilian and military retirees, the congressional plan would limit them to a single increase each July. The White House plan calls for a single annual adjustment in March. Either way retirees would lose about $1 per day in future pension benefits.)

Proposals to force federal and postal workers under social security will not be put forth formally until next year. But people are already anxious about it. They fear that linking the independent civil service retirement system with social security would cut benefits they have worked for, force them to work longer and/or pay more for the same level of benefits already due them.

Ninety-eight percent of those responding said they opposed the cost-of-living cutbacks, and mandatory social security coverage. That was not too surprising.

What was suprising was that tens of thousands of people would take the time to clip, or copy, the questionnaire, sign it often with some juciy comments), address an envelope and stick a 15-cent stamp on it. To measure the volume, remember this is the most mail The Washington Post has ever received on a single subject. That is a lot of mail.

Just as surprising is that 90 percent of the respondents -- and these are so-called timid, apathetic bureaucrats who signed their names and gave their addresses -- said they will vote against Carter and their member of Congress if the cost-of-living cutback goes through.

The mail was heavily from the Washington area. But thousands of letters were postmarked from other places, from Berlin, Md., to Bonn, West Germany. Three came from Caracas, Venezuela; a dozen from London, three from Paris. A lot of mail from Texas, California, New York, Pennsylvania, Georgia (including some from Jimmy Carter's congressional district). And Chicago, Kansas City, Honolulu and Anchorage, Oklahoma City, St. Louis and several from federal employes in Guam.

Some of the mailings were obviously organized. Post cards preprinted by retiree groups. Common address labels from unions. But the organized mail is just now starting to come in. Most of the mail appears to be from real folks, voters and taxpayers who happen to work for Uncle Sam, or who once did. They represent a powerful voting bloc, not only in the Washington suburbs, but in Baltimore, Philadelphia, San Diego, and other big cities with a big federal presence.

The Kennedy people have already responded. President Carter's rival for the Democratic nomination says he will not support the cost-of-living cutback. (Some suggest that's why he carried Montgomery and Prince George's counties in the Maryland presidential primary Tuesday -- the only counties he did win.)

The Republican National Committee is studying its federal pension position. So are some members of Congress who are wondering if balancing the budget this way -- taking inflation raises away from people because of high inflation -- is worth maybe losing their jobs this fall.