The federal pay raise President Carter grants this October will be based almost entirely on political considerations. Nothing else makes sense when deciding the amount Carter will announce within the next two weeks.

Politics will decide whether the raise will be the low-side 6.2 percent, the high-side 13.4 perent, or the odds-on favorite: something in between. Pessemists predict 7.8 percent while optimists say it will go a little over 9 percent.

The raise will be figured into the paychecks of 1 million white-collar U.S. workers, their equivalents in the Veterans Administration and the Foreign Service. Locally, more than 300,000 federal workers will get the October adjustment. Thousands more employes with private firms, unions, and on Capitol Hill could get matching raises.

The presumption that the nation's biggest pay raise -- each 2 percent increase costs $500 million -- will be political makes sense, because no other explanation does.

There are no private industry guidelines to apply to federal workers; most people admit the system Uncle Sam usesto base his pay on the private sector's is badly flawed so that "equity and comparability" are out the window. For example:

The administration put a voluntary ceiling of 9.5 percent for 1980 industry wage gains. Both labor and management generally ignored that ceiling. According to the Labor Department, the average union contract pay raise during the first six months of 1980 was 12.5 percent. So much for voluntary guidelines.

Many people, President Carter amongthem, think the federal payfixing system is unrealistic, and unpopular with the typical taxpayer. It is the only compensation system in the nation that allows its own workers -- from the Labor Department -- to select which industries they will study, and which they will exclude, to compare pay rates.The national survey does not include the country's biggest group of workers, the 12 million state and local government employes. In addition to ignoring those pay rates, the U.S. system does not compare the value of its own fringe benefits -- annual leave, retirement, holidays, insurance, tenure -- with those in the private sector.

Compensation experts from government and industry say that using only selected firms, ignoring local government wages and failing to compare fringe benefits creates an artificial, inflatedpay "gap" every year that makes U.S. workers believe they are vastly underpaid compared with their private-industry counterparts.

Federal unions argue that the pay data collected under the present system is manipulated and scaled down by presidents, whether Republican or Democrat, so that the socalled comparability system never is followed.

Under the existing pay mechanism, federal workers are due a catch-up with-industry raise this October of about 14 percent. Unions say even that figure is low because it doesn't make upfor workers who were short-changed in the past. The Carter administration said a more fair match-up would give federal workers only a 7.8 percent raisethis year.

To further confuse the issue, data collected by the Labor Department for industry wage increases from March 1979, to March 1980, shows an average raise of 9.1 percent.

During the same March-to-March period, the Labor Department says the cost of living was up 14.7 percent. That means the highest raise being considered for federal workerd is less than the actual cost-of-living increase. c

And besides, all those figures are stale by now. So forget about comparability, pay reform, inflation andvoluntary pay ceilings. They are all out the window. So what is left? politics.

Unless he gets a new halo, fast, Jimmy Carter will make his 1980 federal pay decision on the same wave length of Lyndon Johnson, Richard Nixon and Gerald Ford -- by political fine-tuning. He will decide what the traffic will bear, what the public will accept, what the opposition will say, and the minimum amount necessary to keep the federal workers happy.

Presidential aides insist that Carter has not arrived at a final pay figure. Indeed, they say that as late as Friday, the president had not spent even five official minutes thinking about the federal pay raise.

Although federal pay is a multi-million-dollar big deal in Washington, it ranks low on a presidential priority list that includes such tougher items as getting the nomination, freeing the hostages, finding a solution to the problem of one Billy Carter and winning the election.

We will know the amount of the pay increase in a couple of weeks. All we know now is the line of logic that will be used to arrive at it. Politics as usual.