Labor Day this year provides welcome occasion to say something good about America. For most of the anecdotal crankiness about the laziness of the work force finds feeble support in fact.

The irritation reflects expectations dashed as a result of large and long trends in American society. And the way to cope with these trends is by developing broad strategies for achieving the reindustrialization of America.

If the mournful numbers tolled over the decline in the work ethic mean anything, they must mean that Americans are less willing to work. But all the statistics point the other way.

The size of the national work force -- now about 100 million people -- has been rising steadily over the past two decades. During the 1960s it grew at roughly 1.2 percent annually. Now the figure is 2 percent.

The major new participants in the work force are married women. In 1948, only 22 percent of them held jobs. In 1960, it was 31 percent. Now it is over half -- a doubling in 30 years.

Then there are the teen-agers. "Everybody knows teen-agers don't work," the manpower expert Sar Levitan wrote recently. With well-founded sarcasm. For in fact they do work -- and more and more and more. In the past decade alone, the participation of 18- and 19-year-olds in the work force rose from 58 to 67 percent.

To be sure, Americans work shorter hours. Since the turn of the century, according to Dr. Levitan, the average week for full-time workers has dropped from 53 to around 40 hours. But workers produce in those 40 hours five times as much as they used to produce in 53.

No doubt the physical side of the job is also easier. We no longer earn our bread by the sweat of the brow. Nor even by the force of our muscles.

For over the past 75 years there has taken place a long-term swing away from the production of goods in factories and farms and mines and toward the provision of services in offices, banks and hospitals. At the turn of the century 70 percent of the work force was into the production of goods. Now 65 percent make services available.

The shift toward a service economy combines with the changing nature of the labor force to have an adverse impact on output per man-hour, or productivity. Gains in output come relatively easily in an industrial society with almost unlimited scope for absorption of new machinery. They come much harder in a service economy, particularly when a growing fraction of the work force is new to the job.

As a result, increases in productivity have been growing at a lower rate. In the 1950s, the growth averaged around 3 percent annually. It dropped to 2.5 percent in the 1960s and below 2 percent in the present decade. Currently, with recession causing many plants to run below optimum levels, productivity is negative.

In consequence, the country is no longer throwing off the surpluses that used to generate regular increases in wages and salaries. On the contrary, real wages -- that is, corrected for inflation -- have been in decline. At best, they will grow slowly for the next few years.

The onset of slow growth dashes ingrained expectations that life will continue to get better and better at the pace to which we had become accustomed over the past few years. The resulting disillusionment explains the sour temper of the times -- the hostility to headquarters everywhere, but especially in Washington, the itch to return to a supposedly more glorious past.

Unfortunately, there is no way to go backward. The switch to a predominantly service economy is probably irreversible. The period of slow growth is upon us. But the country doesn't need to let its roads and railroads keep declining. It doesn't have to let its steel industry wither, or its auto and rubber industries lose their competitive edge. It is possible by tax and other policies to give those sectors a new lease on life.

It is also possible to drive for productivity in the service sectors. Copying machines and word-processing machines do exist. Semi-skilled workers can be trained to service computers and copiers. And insofar as the training succeeds, pockets of unemployment in heavy industry go down, and productivity gains go up.

The reindustrialization of America, in other words, is feasible. But moving in that direction requires leaders who look forward. Which is why, as 1980 approaches, it is important to assess the candidates with a view to determining whether they are facing toward the past or the future.