Good news for government job hunters, and insiders seeking promotions or slots in other agencies: The federal hiring freeze has been lifted. But it will be some time before Uncle Sam is thawed enough to resume his practice of hiring 380 replacements each day.

Government departments and agencies will get the official word this week that the hiring curb, imposed by President Carter in late October, is over. Except in emergency situations, Carter told agencies they could fill only 50 percent of their full-time vacancies. Officials say it worked, More than 20,000 jobs were left unfilled.

Hiring of temporary and part-timers (not covered by the freeze) shot up during the October through January period. But the number of permanent jobs did drop.

All this does not mean you can rush down to Interior, Justice, HEW or any where else in government and sign on. First off, most hiring officials do not yet know the freeze has been lifted. Formal notification to them could take days or weeks, depending on their place in the pecking order.

The letter to department and agency heads from the Office of Management and Budget advises them that the blanket hiring curb is gone. But some will probably continue a partial freeze, depending on their own individual situation. Agencies with vacancies and with growth planned will resume hiring. Others will proceed cautiously. Some will carry on as if the freeze were still with them.

Mandatory Social Security Coverage: The president's budget does The president's budget does not address the issue. Some callers said they thought they had heard or read that Carter had advocated it. He may later on. But the White House is keeping out of the social security-civil service retirement merger question at least in public.

Several blue-ribbon groups are holding hearings or making studies of extending the Social Security system to include federal and postal employes. Their reports are not due until later this year although indications are some of them may advocate it.

The idea of mandatory Social Security coverage frightens federal and postal employes who signed up with Uncle Sam with the understanding they could retire under their own staff plan. Government worker unions and retiree groups are planning a noholds-barred fight to maintain the independence of the Civil Service Retirement Fund. Hearings on the potential merger will be held here (at the HEW auditorium) today and Thursday. The meeting before the Universal Social Security Coverage Study Group (set up by HEW) is open to the public. Sessions both days begin at 9 a.m. With interest running high, some officials are wondering if the auditorium will be big enough to hold everyone who wants to comment, or listen to the proceedings.

Office of Personnel Management has picked George J. McQuoid to be associate director for agency relations. Other associate directors named to the successor agency to the Civil Service Commission are James H. Gregg for "work force effectiveness and development" and Sally H. Greenberg for "executive personnel and management development." That includes the new Senior Executive Service. Kristine Marcy will be assistant director working with McQuoid.

Nice Work If You Can Get It! Five of the cushiest jobs in federaldom are still standing vacant. Some have been unoccupied for several years.

They are members of the U.S. Postal Service's Board of Governors, a prestige post. Since it was established to help oversee the postal corporation there has never been a fatality linked to overwork. Members get $10,000 a year. They keep their other jobs in industry, and get $300 a day when actually meeting. Travel and expense money is included.

Nine of the 11 members are appointed by the president. They in turn select the postmaster general and deputy PMG who also serve on the board, at straight salary. One would think such jobs would be passed out quickly by the White House, or patronage-hungry senators. But two have been open since 1976, another since 1977 and two more members left in 1978, one after completing his term and another by resignation. Lots of people are wondering why the board is shrinking

Reductions In Force: Budget experts say the job cutbacks planned for a number of departments and agencies will not mean RIFs, except in perhaps two places. They are Defense and Agriculture.