There may be lots of reasons to vote for John Kerry over George Bush, but "job quality" isn't one of them. Kerry has been telling crowds that the country is "shipping jobs overseas and replacing them with jobs that pay you less than the jobs you have today." Ergo, job quality is going to the dogs. A few weeks ago I wrote that presidents have little power to influence job creation. The trouble for Kerry is that they have even less power to alter job "quality" -- the nature of new jobs, how much they pay and how much security they provide. Presidents can't do much more than you or I can.

The composition of U.S. jobs (there are more than 131 million) changes slowly. The Bureau of Labor Statistics divides the labor market into 19 major industry groups. From 1992 to 2002, 12 had employment gains. Even so, the overall distribution of jobs shifted only slightly. Large losses hit farmworkers (who went from 2.1 percent of the total to 1.6 percent) and manufacturing workers (from 13.6 percent to 10.6 percent). Big gains occurred among education and health workers (from 9.6 percent to 11.2 percent) and professional and business service workers (from 8.9 percent to 11.1 percent).

The picture is the same if you look at occupations -- from janitors to engineers. The BLS projects the growth of various occupations. (People in similar occupations work in different industries.) Though some of its estimates will prove wrong, the agency predicts few dramatic changes. From 2002 to 2012, the number of construction workers is expected to rise from 5.6 million to 6.5 million, the number of computer programmers and software engineers from 1.2 million to 1.6 million, and the number of purchasing agents from 419,000 to 455,000. Yes, a changing economy demands new skills and creates new types of jobs. In 1870 almost half the workforce was in farming. But job shifts are gradual.

I suspect that, in a narrow sense, Kerry's claims are half right and half wrong: half wrong because many jobs being lost to other countries are low-skilled and low-paying (that's why they're being lost); and half right because new jobs being created in this recovery may pay less than jobs lost -- mostly for domestic reasons -- in the recession and its aftermath. People who lose their jobs often have to take pay cuts to get new work; the latest BLS study finds a typical wage loss of about 7 percent. In a weak labor market, companies can also hire for a little less. Kerry's charge is plausible, though studies of recent job figures reach differing conclusions. But Kerry's broader message -- the one intended to impress voters -- is wrong.

He implicitly suggests that the U.S. economy under Bush can't create high-paying (aka "good'') jobs. We heard a similar refrain in the 1980s when the United States was supposedly becoming "a nation of hamburger flippers." The story was wrong then, too.

Whatever's happening to wages mostly reflects the temporary effects of the business cycle. The false story survives because it embodies a popular myth: Manufacturing jobs -- which have declined -- are high-paying, and "service" jobs -- which are increasing -- are not. In truth, average hourly earnings for non-supervisory workers in both sectors are roughly similar. In 2003 they were $15.74 for manufacturing and $14.96 for services. Some manufacturing industries are well paid (chemical workers: $18.52 an hour in 2003) and some aren't (apparel workers: $9.56). Some service industries are well paid (financial services: $17.13) and some aren't (retailing: $11.90).

Service jobs now account for more than four-fifths of the total. If all were bad, we'd be a Third World nation. Even if all were bad, a president couldn't make much of a difference. A society's jobs reflect prevailing technologies, consumer tastes, population patterns, workers' skills and government policies. A president controls none of these. Even his influence over government policies is limited, and the effects of government policies are themselves limited.

What can government do? Suppose it turned rabidly protectionist; that would mainly aid manufacturing, involving about 11 percent of all jobs -- and all consumers would pay higher prices. Suppose government raised the minimum wage; well, that might help some low-paid workers -- but others might be priced out of a job.

Suppose government required that companies provide more health insurance for workers; well, most of the extra costs would come out of wages. Suppose that government magically improved the quality of schools; well, that might qualify more workers for higher-skilled and better-paid jobs -- in about 10 or 15 years.

It's easy to make speeches about jobs; but it's not easy to affect jobs. John Kerry and George Bush have genuine differences over taxes, health care, energy policy and judicial appointments. There are legitimate questions about their foreign policies, leadership styles and characters. Voters should decide based on real issues, not rhetorical flourishes.