The global economy is at one of those critical junctures where stagnation threatens to take hold again, unless the governmental authorities in Europe and Japan follow bolder policies to stimulate growth and employment.

Treasury Secretary James A. Baker III, and officials of the Paris-based Organization for Economic Cooperation and Development weren't successful in making this point at last week's ministerial meeting.

But in wake of the unexpectedly slow growth of the American economy in the first quarter (only 1.3 percent), a faster pace -- especially in Western Europe -- becomes a critical need and has automatically moved this issue to the top of the agenda for next month's economic summit in Bonn.

The turn of events has grim implications, as well, for Third World countries, whose hopes for recovery have been pinned critically on sustained real growth rates of about 3 1/2 percent in the richer industrial nations that buy their manufactured goods and raw materials. For the past two years, the American economy has been the locomotive pulling the world out of recession. What happens when the locomotive loses power?

The 3 1/2 to 4 percent American growth rate that the Baker team confidently had been forecasting for 1985 may now be out of reach. And because so much of Europe's present 2 1/2 to 3 percent pace depends on huge exports to the United States -- which now may fall off -- it will take some serious stimulative moves in Europe such as tax reductions to prevent European unemployment rates from deteriorating further.

Although the poor report on first-quarter gross national product should reduce the Reagan administration's boastful rhetoric of recent months, it still is difficult to spend a week in Europe, as I just did, without making comparisons with our own economy, and thereby being reminded of how far most European countries must go to catch up.

Secretary of Commerce Malcolm Baldrige apparently bruised some sensitivities when he laid this case on the table at a meeting of European bigwigs in Venice last week. But the figures speak for themselves: Since 1970, the American economy has added 27 million jobs; the European economies, zero. You might say that's an old story. And true enough, it has become a cliche' to talk of Europessimism or Eurosclerosis. But this time, I sensed two important differences:

First, many major European countries have made strides in boosting their economic pace (partly benefiting from exports to the United States). Their inflation rates have come down, and wage scales are less hopelessly rigid.

And second, European politicians, businessmen and labor leaders all have decided that maybe there is a bit of magic in the tax-cutting, market-oriented policies Ronald Reagan has been selling in the United States, whether you call it supply-side or Keynesian economics.

Looking at the communique' issued by the OECD at the end of its meeting, a Reagan administration official noted with satisfaction the stress placed on getting rid of archaic business regulations and labor laws that inhibit creation of job-generating businesses.

But the problem for Europe is that it isn't all that easy to change. There are just as many cultural barriers in Europe to matching American marketing and production techniques as there are in Japan. The kind of labor mobility so commonplace in the continental United States is simply unknown in Europe.

"If you were born in a coal town in Wales, it was expected that you'd stay in Wales and dig coal," a Welshman who escaped to better things in Paris told me.

The great impediment for Europe is that, compared with the United States, it is a continent of small countries, each of which -- out of national pride and a rich, significant history -- thinks of itself as bigger and more important than it really is. As a Common Market composed of 11 nations, it still is not able to act as a powerful entity, and the stronger powers among them -- Germany, France and Britain -- have many mutual rivalries, suspicions and distrusts.

In West Germany -- the strongest economic power in Europe -- the economy is the No. 1 political issue. There is a dangerously stagnant birth rate, unemployment of about 10 percent and a still costly welfare state (the social security system is in financial jeopardy). What's more, political scandals have shaken the public's faith in the government. Yet, the Kohl government is quite content to go along with a growth rate of less than 3 percent, even though that means no reduction in the jobless rate.

Because of restrictive work rules in the unionized sectors throughout Europe, and hostile labor-management relations, labor has just about priced itself out of the market, especially in manufacturing industries.

In France, for example, where the growth rate is only 2 percent, if a company wants to fire 50 or more workers, it has to wait a year to do it. Of course, such laws had good intentions. But instead of protecting jobs in Europe, they have the effect of blocking new ones: Employers don't hire freely knowing that layoffs can't be pursued easily.

The unexpected decline in the prospect for GNP in the United States -- a reflection of the fact that more American business and profits than ever before are going abroad -- adds a new element of urgency to a real European revival, and makes the Bonn summit one of the potentially most significant in recent years.