Oh sure, kick a party when it's down. Noranda Forest Chairman Adam Zimmerman's tough speech to Ontario Liberals last week (''rather than wasting your time hurling insults in Parliament . . . why not study and really learn these issues?'') has set off a round of stern lectures about the need for the Grits to make nice with business again.

''The Liberal party has blotted its copybooks with the business community,'' Alcan's David Culver says. The same lament has been taken up by editorial writers. Those dreadful Liberals. All that interventionist and protectionist rhetoric. How could they turn on their friends in the business community like that? No wonder they're in debt.

This is a lover's quarrel if ever there was one. Business feels as if it hardly knows the Liberals any more. The party is cold, it's diffident, it's been avoiding business in the halls. That man Turner seems particularly to have jilted them. ''I thought he would lead us back to our traditional positions, away from economic nationalism,'' complains Harris Steel Chairman Milt Harris. ''I thought . . .''

They haven't given back the ring just yet, though. For all the supposed rift between the Liberals and big business, the donations keep on coming: $5.3 million in 1987, compared with $6.7 million for the Tories. It was individual donations that fell away, leaving the Liberals, oddly enough, more dependent on big business than any other party.

The business community is feeling almost priggishly self-righteous these days, after the success of the free trade campaign. Now, it's nice that business was on the side of light and understanding in the free trade debate - this time. But the reason business supported the deal was that the Tories held out the promise of access to the U.S.

FLAMING RHETORIC

Had the government simply lowered our own trade barriers unilaterally, which would have achieved much - perhaps most - of the gains from free trade, business would have been as flaming in its rhetoric against the deal as Turner ever was.

Likewise on the deficit. If this budget did any good, it was to explode the myth that all our fiscal problems would be solved by doing away with universality. Well, we've done that, and it's saved us all of $320 million.

But if one turns to subsidies to business, one finds $11 billion, more or less untouched. Perhaps $3 billion of this serves some useful social purpose. But cut the rest, and the deficit's down, without tax increases or closed military bases.

The truth is, business and politics have been corrupting each other in this country ever since the days of Hugh Allan and the Welland Canal, when the cabinet of a province and the board of directors of the local railway typically met concurrently.

I don't notice Zimmerman denouncing the artifically low stumpage fees forestry firms have historically paid provincial governments. I haven't heard Harris preaching free trade to his steel industry buddies, who are now lobbying for limits on imported steel. Those corporate bigwigs on the Premier's Council in Ontario seem as keen on central planning as any old Herb, Lloyd or Sheila.

It is hardly fair for business to carp if this cozy relationship occasionally cloys. It was agitation in the oil patch for ''Canadianization'' that was the original impetus for what became the hated National Energy Program, just as it is the Association of Canadian Publishers that has been loudest in support of the present government's re-enactment of the NEP in the publishing industry. They will some day be denouncing the same policy.

The knock against the Liberals is not now, nor has it ever been, that the party is too concerned with the poor. It is rather that the Liberal party, like the others, has been ready to entertain any scheme concocted by producer interests to raise prices or otherwise distort the market to their own advantage: all the marketing boards and import barriers and ''regional development'' handouts that all three parties staunchly support.

The poor inevitably bear a disproportionately large share of the costs, and receive a disproportionately small share of the benefits of these scams, with the result that, though our tax and transfer system is modestly progressive, its effects are canceled out. And nobody in politics breathes a word.

The distribution of income is no better now than it was 30 years ago; 3.5 million Canadians remain below the poverty line. More than two million of them are voters. There's the constituency Liberals should pursue.