WHEN YOU'RE worrying about traffic control at overcrowded airports, curbing the mishandling of hazardous chemicals, controlling illegal drug traffic and immigration or monitoring food, drug and toy safety, it's easy to forget that the people who do these useful things are federal civil servants -- people who are now No. 1 on the administration's hit list.

The administration's current budget plans call for a 5 percent cut in federal pay in 1986. With inflation running about 5 percent, and below-inflation raises in 1985 and 1987, this would amount to almost a 15 percent loss in purchasing power -- not counting cuts in pensions and other benefits. The Office of Personnel Management has suggested that the "only realistic alternative" to the pay cut would be to lay off 125,000 federal workers -- never mind whether their services are needed.

At his recent press conference, President Reagan said he thought the pay cut was fair because workers in some declining industries had taken pay cuts and because some high-level appointees have made proportionately larger financial sacrifices to enter government service. The Office of Personnel Management makes a different argument -- it justifies the pay cut by asserting that not enough federal workers quit the government. Since pay is a major factor in decisions to leave jobs, OPM concludes that federal pay must be too high.

One reason, of course, that federal "quit rates," as they are called, might be lower (the data are disputed) is that the government is so big it can provide many more opportunities for job-switching (which doesn't count as quitting) and promotion than all but the very largest private firms. Small firms, which dominate private-sector data, typically have much higher turnover than large firms. The federal work force, moreover, doesn't include high turnover occupations, such as retail and construction workers, which drive up the private-sector average.

But even if you could control these things, it would not be surprising if government "quit rates" were significantly lower simply because the civil service compensation structure is set up to promote retaining workers. Traditionally, civil servants have been offered higher job security -- backed up by relatively generous pensions -- in return for lower pay. A recent study by the Hay Group, widely respected consultants on private- sector compensation, confirms that this trade-off still operates -- federal workers earn about 10 percent less on average than comparable private workers and have inferior health benefits. But superior pensions reduce the federal disadvantage to about 7 percent of private compensation.

OPM correctly observes that some technical and professional workers are underpaid by government while workers in other less-skilled categories tend to be overpaid. But its idea of basing pay on "quit rates" is a bad one, since it would tend to give higher raises to just those lower-level clerical occupations where pay is already relatively high. No doubt there is much room for improving federal personnel policies, but OPM hasn't made its case.