Dwellers in the United States of America must for another three weeks endure the normal, biennial extravagance of a political campaign in which rival candidates vie in mythological inventiveness.
Probably the departure from objective fact is no worse this time than normal. It just seems that way because we tend to forget in between times how irrational campaign rhetoric can be. But as I listen to President Reagan blaming 10 percent unemployment in the US on ''spendthrift'' Democrats from Franklin Delano Roosevelt through Jimmy Carter and then listen to Democrats reversing the plot and blaming it all on Mr. Rea-gan's ''heartlessness'' - I yearn for a touch of quiet reasonableness.
Where does the blame, if there is blame, really lie?
There are certain facts which can give us a fix on some of the main causes for today's apparent ills. I use the word ''apparent'' intentionally. Much of these supposed ''ills'' are nothing more than a difference between today and some point in the past which may be just as untypical as today.
There are three main facts about the present American condition. One is high unemployment. Another is a decline in economic productiveness. The third is a population which continues to grow, much of it by immigration. And much of that is illegal.
Many Americans, and many others as well, have long been accustomed to thinking of the US as being the wealthiest country on Earth. For much of this century it has been at least one of the wealthiest on a per capita basis. But that was partly because its ratio of people to wealth was in better balance in the early and middle parts of the century than it is now.
There has been an enormous increase in population during the century. The figure was 76 million in 1900. It was 226 million in 1980. The figure was still under 110 million at the time of World War I. It has more than doubled between 1920 and now.
Relative US productivity went up enormously during and for a short time after World War II, due to an unusual circumstance. So much of the rest of the world was damaged or disorganized by the war that an unusual demand existed for American goods. The US became accustomed both to a high overseas demand for its products and to high returns from the existing industrial fabric of the country.
Factories built before or during the war continued to meet the needs of those times. There was no need to build new factories using the latest technology so long as the old ones continued to turn out what the market would absorb. And that meant continued high employment - high enough to keep up with a rising population.
But the condition was abnormal, not normal. It came to a painful end when such other countries as West Germany and Japan replaced their bombed-out factories with the lastest and best in modern technology. There was a shrinking of demand for American products while the US population continued to grow. Obsolete factories, declining demand, and a rise in population equalled a lower level of per capita material wealth, and rising unemployment.
Neither Republicans nor Democrats are responsible for the lag in modern factory building, the decline in world demand for US goods, or the rise in the US population which lie behind today's relatively high rate of unemployment (half what the level was in the Great Depression of the '30s).
But Republicans and Democrats are equally responsible, along with most other Americans, for not realizing at the time that they were all living in abnormal conditions and that the prosperity which those conditions produced would not continue indefinitely unless drastic measures were taken. And even if the leaders of either or both parties had realized the conditions of the '50s as abnormal they would have been unable to persuade the Congress or public opinion to take the necessary and drastic steps to fend off the conditions of today.
So today the US is not the wealthiest country on Earth in per capita terms, but only the 13th. Top country according to the latest edition of ''The World in Figures'' (The Economist, London) is the United Arab Emirates, with a per capita wealth of $19,000 a year, as compared to the US at $9,637.
If you are interested, the second is Kuwait, then Lichtenstein, Switzerland, Monaco, Luxembourg, Denmark, West Germany, Sweden, Jersey, Belgium, and Qatar.
The leading 12, be it noted, all have relatively small populations. West Germany is the only big country ahead of the US, which may be of some consolation, to both.
Now back to the hustings where, of course, it is all the fault of Democrats - or Republicans. Take your choice.