TO JUDGE from the press releases and news stories on monthly unemployment rates, you might suppose that the number of jobs in the nation has shrunk in recent years. Actually, there were 5 million more non-farm jobs in February 1983 than in 1977, according to the Bureau of Labor Statistics, a rise of 6 percent. And these figures probably understate the long-term growth in employment, because they compare a period of recovery with a trough at the bottom of an employment cycle.

But the picture is far from uniform all over the country. It probably won't surprise you that in Michigan, home of the troubled auto industry, employment was down 9 percent in that period, while in Texas, the headquarters of the oil industry, the number of non- agricultural jobs rose 25 percent. You don't have to strain your imagination hard to picture thousands of "black tag people," as Texans call arrivals from Michigan, with its black license plates, searching for jobs in a new and not always congenial environment.

But Michigan is not the only state that has lost jobs. The number of non-agricultural jobs is down 4 percent or more in the whole string of industrial states from Pennsylvania and West Virginia, west through Ohio, Indiana, Illinois and Iowa; the reason is the apparently irreversible decline in the auto, steel, rubber and farm machinery industries. And there has been little if any growth in jobs in most surrounding states. It is as if the center of the nation were emptying out, with growth in the periphery, up and down the East Coast, around the Gulf of Mexico and in the Southwest.

The big gainers have been not only the oil states of Texas, Oklahoma and Louisiana; the Southeast has done well, especially Georgia and Florida. And New England, New York and New Jersey, once trouble spots, have all gained jobs. The Pacific Northwest is in trouble because of the ailing lumber industry, but California, Nevada, Arizona and Colorado continue to have rapidly growing economies.

Why has unemployment risen even though the economy has generated more jobs? The answer is that the labor force been increasing more rapidly during the past few years than it has at any time since the first decade of this century. The economy has had the difficult task of coming up with enough entry-level jobs for the extraordinarily large number of baby-boomers who have been entering adulthood and the work force, for the unprecedentedly large percentage of women who are seeking jobs, and for the immigrants who are more numerous than at any time in the past 50 years. To a greater extent than is generally appreciated, the economy has performed this task.

Now the task may be getting easier: people born in 1957, the peak year of the baby boom, turn 26 this year, and most of them have entered the labor force; immigration may be tapering off in response to the slowdown in the U.S. economy. Difficult problems remain: we need more economic growth and we need to address the special problems of the industrial heartland. But we should not forget what the economy has shown itself capable of doing.