In Britain, a Labor government struggles to contain wage demands and squeezes the money supply in Conservative fashion.

In Sweden, a "bourgeois" coalition last year poured out a flood of subsidies and spending to preserve the full employment heritage or its national rivals, the Social Democrats.

In Denmark, Anker Joergensen, a former union chief and now Social Democratic premier, brings the Liberals, his nominal competitors,into a coalition to withstand pay demands.

These role reversals are a commonplace in northern Europe's tier of stable democarcies. Programs, platforms, manifestog give way in office to stubborn facts of life. Fiorello La Guardia, who once insisted there was neither a Democratic nor a Republican way of assuring a city's water supply, would have enjoyed the spectacle.

In an earlier time, The Economist coined the useful label "But-skellism," an amalgam of Tory chancellor R.A. (Rab) Butler and his Labor shadow, Hugh Gaitskell. It implied that their economic policies -- as distinct from rhetoric -- were indistinguishable.

This sort of thing is not unknownn in the United States, where the less partisan long ago boserved that the behavior of Democrats and Republicans in the White House was roughly similar.A Republican, Herbert Hoover, launches a new interventionist deal with the Reconstruction Finance Corp.; a Democrat, Franklin D. Roosevelt, briefly meets but is little influenced by Keynes and keeps a lid on spending until the war. More recently, Republican Nixon imposes price and wage controls while Democrat Carter curbs social outlays.

The naively cynical will say that this simply reflects what everybody knows, that politicians are opportunists. They might recall the American folk wisdom that platforms are to run on, not to stand on.

But this is incomplete, too shallow an explanation. A stable socity, one whose institutions are reasonably secure against overthrow, will not move abruptly right or left when office changes hands. Its citizens are mostly agreed on fundamental issues, at home and abroad. Its politicians are limited to competing for office through a debate over questions at the margin.

In all the stable democracies of Europe's northern tier -- Britain, Norway, Denmark, Sweden and Holland -- this broad consensus exists. This agreement is a necessary condition for stability and helps explain the undramatic behavior of parties. *tDomestically, there is a preference for private property, buttressed by a scaffolding of law. Market forces are relied upon to set most levels of price and output. But there is no mystical attachment to either and no inconsistency seen in permitting the state to monopolize public utilities and run some industries or corporations.

There is widespread agreement that the state must insure minimum standards of health, housing and a tolerable old age. There is equally broad agreement that the state must intervene to keep the economy on something approaching an even course, through tax, spending and money policies.

Finally, in all the stable northern democracies, there is a general conviction that the good life depends on more or less free expression of opinion and equal access, in theory, to the political and judicial machinery.

There are challenges to all these propositions from fringe groups on the left or right. But even in the four countries with proportional representation -- all but Britain -- the challengers elect only a handful of legislators.

Another trait or stable democracies is that they are essentially at one with their history. There is no pervasive uncase, guilt or shame, acknowledged or denied. The lack of this quality still raises questions about the future of democracy in West Germany. Years of Prosperity

FOR THE FIRST quarter century after the war, the three large and less solid democracies -- Germany, Italy and France -- led the West in an outpouring of goods and services. But their more politically stable neighbors also enjoyed record if less striking prosperity, as did the United States.

The last five years have changed all this. Growth has been slow and uneven. Jobless totals have climbed everywhere except in Scandinavia. No nation, with the recent exception of the Germans, has been immune from an inflationary disease that each year clips one-twelfth or one-tenth from the value of the currency.

And yet the fabric has held together. Even more curious, three southern European nations, Greece, Spain and Portugal, threw off or escaped from totalitarian regimes to work out a recognizably democratic order.

There is another way in which the bleak performance of the last half decade can be seen. It may be that consensus politics survived because citizens sensed that the economic order has demonstrated astonishing resilience.

The system has absorbed without catastrophe soem heavy blows. The international monetary order was abolished in August 1971. A drastic increase in oil prices created dramatic surpluses in oil countries and matching deficits in the West.

The Organization for Economic Cooperation and Development named some wise men to see if the system was fundamentally unsound. They disarmingly concluded that, no it was not, it had merely been victimized by a series of coincidences -- oil, drought, sloppy fiscal and monetary policies.

The wise men barely touched on or ignored the central lessons of the last five years. This period laid bare the two strains that are the source of continuing debate in the European democracies and emerging onto center stage in the United States.

One is internal -- the power of large corporations and unions to resist all but the most disastrous fiscal and monetary policies and thus drive up prices and wages. In good times and bad, both groups tend to drive inflation forward at intolerable rates. Even a drastic curb on the money supply or government outlays need not stop them.

The inflationary potential of institutions enjoying near-monopoly power is a genuine threat to the stable consensus in Europe's nothern tier, and the search for a solution is the major topic of debate.

Abroad, the past five years have seen a new threat to stability, the emergence of genuinely developing nations. Brazil, South Korea, Taiwan, Hong Kong and even India are producing ships, steel, textiles and some machinery more cheaply than the traditional industrial states.

The first and inevitable political response is "lock the gates." So "voluntary agreements, safety regulations, quotas, tariffs and, now, a new device, the minimum selling price, are all employed to shut the ports.

In the past it was fashionable to argue that closing markets to the Third World was dangerous, that somehow hordes of outraged Brazilians, Indians and Taiwanese would descend on the West. Nobody need believe this today.

But it is certainly arguable that a sullen Third World, resentful of sealed markets, could make the West and North a less comfortable place to live, could inspire dangerous adventures. A New Burden on Growth

WHAT THEN are the northern democracies' prospects for continued aurvival? A biologist might answer that it depends on their ability to adapt to changing circumstances. This suggests they must find some orderly, institutionalized way of dividing the pie. They must abandon the belief that uninhibited collective bargaining is compatible with strong unions, that unfettered pricing power is consistent with industries dominated by a few firms. (One approach, reducing corporations and unions to innumerable competitors -- antitrust everywhere is not on any serious European agenda.)

The running debate in the northern tier over income policy; over giving workers a role in corporate decisions; pay and price restraint, guidelines and norms, all reflect this concern.

Adaptation also suggests accepting gradually the tide of manufactured products flowing from the south, and slowly dismantling the barriers built against them to ease men, plants and land into sectors where the West enjoys great advantage -- the production of computers and other manufactures of high scientific content; the vast and growing range of services in demand around the globe, education, medicine, information, banking, insurance and more.

If obsolete and inefficient industries are preserved -- a tempting strategy -- a new burden will be placed on growth. In time, incomes that are now rising at a relatively show rate will level off and ultimately decline. It is not clear that the democratic consensus could stand such strains. Expectations may have been dampened in the past five years but they have not been stified. A steady fall in citizens command over goods and services would inspire new politicians with fresh solutions and new followers. There is no reasons to think they would find much value in competing on the traditional democratic grounds.

But resistance to change is strong. Corporate and union chiefs feel diminished when they must subject decisions they customarily make themselves to another body, social or governmental. No worker will readily accept the loss of a job or skill. This is why any shift is likely to take place slowly.

The resilience, the toughness of both the economic and political structure in the northern tier offers some grounds for belief that adaptation will be made. But only some. A Hungarian proverb holds that the difference between an optimist and pessimist is that the pessimist is better informed. Or as, Damon Runyon's Sam the Ganef remarked, "I long ago came to the conclusion that all life is 6 to 5 against."