The federal budget President Reagan sends Congress today will ask it to authorize 63,182 fewer jobs in non-Defense agencies over the next 18 months than President Carter requested in his final budget. Reagan's budget will propose more Defense civilian hiring than Carter wanted.

But despite the precision of the numbers, it could be weeks before government agencies can translate the proposed Reagan cuts -- which are cuts from Carter proposals -- into reality. It will take time before most agencies know if they must continue their hiring freeze, if they can resume hiring or if the cuts -- if Congress okays them -- will force them to resort to RIFs (layoffs) or how many people will be RIFed.

The Reagan budget will be followed by "allotment letters" to government offices spelling out new (mostly lower) proposed ceilings on dollars, program changes, such as major shifts of grants authority, could force agencies to RIF or to keep the freeze on to cut personnel via attrition.

The budget cuts are hard to translate into warm bodies because they are based on the assumption Congress will approve them intact (it rarely does) and because Reagan's cuts are based on projections -- not actual current job totals -- left behind by Carter.

Many federal agencies have wargamed the Reagan cuts to predict what they MIGHT have to do if Congress goes along. Examples:

Public Health Service, with 25,000 workers in metro Washington, has advised senior officials that it would have to cut 6,000 jobs over the next 18 months if it bears the full brunt of cuts in dollars, programs and people the president will propose for it. PHS has just over 52,000 workers nationwide.

Economic Regulatory Administration (part of the Energy Department) will be told to take the drastic budget cuts -- subject to congressional approval -- that could force it to reduce its current staff of 1,600 to 400.

The 63,000 non-Defense job cut Reagan will propose breaks down to a reduction (from the Carter budget projections) of about 32,000 positions by the end of this fiscal year (Sept. 30) and another 31,000 during the 1982 fiscal year that ends Sept. 30, 1982. But those cutbacks will be offset by job increases in Defense.

The Defense increase and non-Defense decreases would reduce federal employment in fiscal 1982 about 43,000 jobs below those projected by Carter. What that translates into in terms of actual employment is anybody's guess.

American Federation of Government Employees has placed one of its showcase units, the 2,000 member Local 12 at the Labor Department, in trusteeship. That means the local will be run by the AFGE national office until the trusteeship is ended.Local 12 has had financial problems, and been troubled by faction-fighting. It has also negotiated some of the best, most liberal contracts in the federal service.

One problem, officials at the national office say, is that the local's dues structure has been too low to meet the monthly $5.10 per member per capita tax to be the national AFGE. Trustee John Sturdivant, assistant to AFGE's national vice president, has reappointed the local's new president, Bettyjane Lumpkin, and chief steward Chuck Wood. He plans to hold a series of meetings with members of the local to iron out problems leading to returning control of the Labor unit to local officers.