More than 100,000 federal and military retirees here will be getting a $5 million a month increase in their annuity and pension checks effective March 1.

The 4.8 per cent inflation adjustment will first show up in checks mailed for early April delivery to government retirees here and to the million-plus ex-civilian and military aides or their survivors worldwide.

The before-taxes increase in pension checks will boost the monthly government payout to civilian retirees here to $105 million, and raise the worldwide total of government civilian pension payments by about $34 million, to just over $700 million a month.

Retired federal civilian and military employees and their designated survivors are guaranteed regular cost-of-living raises designed to keep them relatively current with inflation as measured by the Consumer Price Index.

The CPI for December, which was released yesterday, hit 174.3. That, the government says, represents a 4.8 per cent increase over December of 1975 and is the basis for the increase.

From 1969 until last year, retirees got increases on an irregular schedule whenever the CPI went up by 3 per cent over the amount of the last increase and remained at that level or higher for three consecutive months.

Congress changed that system, partly because the rate of inflation had increased the frequency of the raises, and partly because the cost of a 1 per cent "sweetener" added to each CPI boost to make up for the time lag was criticized.

In its place, Congress set up a system whereby retirees are guaranteed two cost-of-living adjustments each year - on March 1 and Sept. 1 - and dropped the extra 1 per cent. The coming March raise of 4.8 per cent will be the first increase under the new system.

The 4.8 per cent raise is a gross increase before any federal or state taxes are imposed. Federal officials say the $5 million monthly increase estimate is conservative because it covers only the estimated 70,000 civilian federal retirees here.

There are about 30,000 retired military personnel in the area and the 4.8 per cent increase that they will get at the same time will increase substantially the actual value of the pay out. The increases are automatic and retirees do not need to apply for them or call their former federal agencies.

Housing and Urban Development: National Federation of Federal Employees has gone to U.S. District Court here hoping to block several HUD reorganizations and employee job transfers. NFFE says some of the moves appear to be inspired by lameduck Republican appointees seeking to sabotage programs and/or carve out jobs that are "safe" from replacement by the Democrats. It also says some downgrading actions haven't been done properly.

Kill the Pay Raise: Rep. Charles Grassley (R-Iowa) has introduced legislation to block the 28 per cent average pay raise former President Ford proposed for top elected and appointed federal officials and judges. The boosts - unless Congress disapproves them within 30 days - would go in to 20,000 career federal executives who are now at the $39,600 pay ceiling.

American Federation of Government Employees has switched its membership newspaper - The Government Standard - to a new format. The more compact, but fatter, paper is one of the largest weeklies in the U.S., going to nearly 300,000 members.

Rumor Department: Federal officials in New England keep hearing rumors of a possible merger between the independent National Association of Government Employees and AFL-CIO's American Federation of Government Employees. NAGE president Kenneth T. Lyons is based in Boston. The two unions have cooperated recently in a political drive to help the Carter-Mondale ticket and they've had discussions about merger but nothing official, final or solid yet, both sides say.

Go To Work Friday: A number of workers have called to say they've heard that Friday will be a holiday (today is) for government workers here. Others have suggested that it would be expensive and troublesome for federal offices that are shutdown today to reopen, and crank up the heat for one day of work. Federal officials say it is no problem - so go to work.