Summit song of prosperity is not the whole show. Tune could change by year's end as untackled problems close in

The leaders of the seven major industrial democracies gathered in Toronto over the past week and congratulated themselves on having achieved ``the longest period of economic growth in postwar history.'' They probably could have been even more lyrical about the immediate condition of these favored seven.

Seldom if ever has there been such a widespread sense of peace and prosperity among the citizens of the seven. There is at the moment a remarkable degree of stability and comfort and affluence for them and among them.

Most of the people of Western Europe, North America, and Japan are living amid rising economic well being. And for the moment the dark cloud of East-West tension has been dispelled from overhead. The sunshine of the recent Gorbachev-Reagan summit was still beaming over the seven at Toronto.

The fact that a majority of the people of the world live outside the comfort and contentment of the seven, and that there are fearsome fissures in the foundations, did not intrude upon the contentment and beaming self-satisfaction of those who chatted and dined together in these halcyon days at Toronto.

Let them, and let all of us, enjoy this while it lasts. Their successors are all too likely to be looking wistfully back at June of 1988.

``Peace and prosperity.'' It is the magic formula for political success. We of the favored seven have it, right now. One question is whether it will last through to the end of the year.

That matters greatly for two Americans - George Bush and Michael Dukakis. One of the two will presumably be speaking for the United States at the next economic summit. Which one will almost certainly depend on whether this broad sense of peace and prosperity survives through election day in November.

Before the next four years are out the winner may wish that he had been the loser in 1988.

The welfare of the seven depends too heavily for comfort on the prosperity of the US. But US prosperity depends too heavily for comfort on the flow of foreign funds into the US. Can the federal deficit and the imbalance in American trade be cured before foreigners either withdraw their funds or cease lending by investing so generously?

One ray of sunshine has just fallen on this problem. The biggest item in the US budget has been the President's huge military buildup. Any doubt as to whether this will be slowed down has been removed by the disclosure of massive improprieties in Pentagon purchasing procedures.

The ``military-industrial complex'' which President Dwight Eisenhower warned against in his farewell address has hurt itself. It has a newly earned bad reputation.

So there will be new economies in the military budget.

There will be tighter scrutiny of every military contract.

The deficit and the imbalance in trade, however, will not disappear by November. Both will be an urgent problem on the desk of the next US president. And along with that will be the emerging importance of doing what may be necessary to save this planet from the ravages of mankind.

No one is quite sure whether pollution of the atmosphere, deforestation, and overuse of water have contributed to the current drought in the US.

But we all know now that unless we can salvage our forests, our water supply, and our air from industrial abuse and overpopulation, there will be an unpleasant day of reckoning when the planet will no longer be able to sustain humanity.

The politicians have yet to come to terms with this vast problem of the future.

President Reagan hasn't really tried to persuade the United States Congress to do what is necessary to reduce the flow of industrial pollution from the American Midwest to the acid rains of the Northeast. He hasn't really tried. His successor will have to worry about this.

The nations have yet to consult together adequately to save the rain forests of Brazil, Africa, and Asia, to reverse the creeping spread of deserts, to clean up the air man must breathe.

But to turn back to what the politicians of today have done.

The seven favored countries (the United States, Canada, the United Kingdom, France, West Germany, Italy, and Japan) have been able to bring their economies largely undamaged through the sudden descent of the stock markets in October, 1987.

They have been able to avoid a disastrous turn to trade protectionism. They have been able to keep their currencies interchangeable. And the immediate danger of a nuclear war between the US and the Soviet Union has been removed from over their collective heads.

Toronto proved that the nations have learned something from the economic disaster of the Great Depression of the 1930s and the human disaster of World War II. The seven leaders there could congratulate themselves justifiably on making their countries more prosperous and less in danger of war than they these seven were in 1914 or 1939. There is neither economic disaster nor another World War on the immediate horizon.

The miseries of the Middle East, starvation in northeast Africa, violent war in the Gulf and in Afghanistan, political and economic deterioration in Central America were overlooked during the love feast in Toronto.

All those and more will be with us for a while.