The Canadian business community may not realize it yet, but they have all been nationalized. Or perhaps drafted. Ontario Premier David Peterson warns that ''Canada's leading high technology firms'' are being swallowed up by foreigners. ''What will our response be,'' he asks, ''if two of our jewels, Spar Aerospace or Northern Telecom, are faced with takeovers?''

Meanwhile, the Canadian Manufacturers' Association is girding for war. ''National economies are engaged in a silent war in the marketplaces of the world,'' says the CMA in its recent report, The Aggressive Economy. The CMA's ideal is ''an economy in which all resources are aligned behind a central objective. This turns out to mean a raft of tax breaks for - guess who - manufacturers, who are relentlessly described as ''the engine of growth,'' if only for their ability to rack up trade surpluses.

There are several words for this concept of the economy: ''corporatism'' and ''mercantilism'' are kindest. It is one in which ownership is in private hands, but control rests with the state. That power is in turn devoted to the support of favored corporations, industries and sectors, with whom the national interest is identified. It is an alliance of the self-interest of the recipients and the pretensions of their patrons, and, notwithstanding the claims of its proponents, there is nothing new or rational about it.

BASIC MISCONCEPTIONS

There are some pretty basic misconceptions at work here, so let's work on the fundamentals. Manufacturing is in no meaningful sense more the ''engine of growth'' than services or any other sector. An economy is not a machine, made up of several discrete components, each working to the same end. It can more be thought of as an organism, the living interaction of millions of separate decision makers, each with their own goals in mind and their own chosen avenue to pursue them.

Economics passes no judgment on what those goals should be: whether people should save more or less, whether growth should be fast or slow, whether they should export or import, manufacture or serve, work with their hands or their heads or their hearts. It only says they should have whatever makes them happy, so long as their choices are made in full awareness of the constraint of scarcity: more of one means less of another.

Unless it can be shown the market is not performing its role of reflecting consumer preferences under scarcity - and in some cases clearly it does not - then it serves no good purpose to divert economic activity from the course it would naturally follow. All one achieves is to force consumers and producers to choose an allocation of resources which, though it may be the best available to them under the circumstances, is not what they would have selected in the absence of such interference, and hence must be less pleasing to them.

There are things the market cannot do, that only government can. But there ought to be no presumption that those in government have any greater ability to discern future patterns of consumption or returns to investment - the explicit or implicit belief underlying all industrial ''strategies'' - than that of those whose livelihood depends directly on it. The presumption should be the opposite.

The error is not in governments subsidizing losers instead of winners, or of propping up sunset industries instead of infants. Whether the industry is economic or not is unimportant.

If an economy is not a single unit, with a single purpose, then it makes no sense to talk as if Canada were competing with Japan, or the U.S., or any other economy. Individual Canadian companies, or industries, of course are in competition with their counterparts abroad. But the combination of economies through trade is opposite in effect. Far from competition, it is a process of co- operation, allowing producers in each economy greater scope to specialize in what they do best, and consumers greater diversity of choice.

Corporations are neither footsoldiers in an international economic war, nor ''jewels'' to be kept jealously guarded within one's borders. They are independent economic agents, whose fortunes are their own to watch over, whose survival should depend strictly on whether they are efficient and responsive to consumer demand, whose master in those things that are the market's concern should be only the market.