It is a peculiarly Canadian irony that the last man of principle in our politics should be found hiding in the Senate. Had not fortune flushed him out, he might never have been discovered: who'd have thought to look for him there?

Purists might prefer that George van Roggen were an opponent of free trade, who still felt such ties to democracy as would forbid him leave to play John Turner's game of constitutional chicken. Van Roggen, in fact, had rather hoped just to keep quiet as the free trade bill rolled through Commons and Senate into law, betraying neither his leader nor his conscience.

But high crises in affairs of state are not often tolerant of strategies of silence: Sir Thomas More hoped the same, and look where it got him. Turner's call to inaction forced the Senate Foreign Affairs Committee chairman to choose, if not between free trade and democracy, then between party and principle, and of van Roggen let it be said he chose principle.

Few others come out of this business looking as well. Constitutional considerations have been drowned in the undertow of opinions on the Free Trade Agreement. Those who favor the deal have been uniform in attacking Turner's gambit; those who oppose the deal have almost to a man defended him. (Ed Broadbent, after a day or two of calculation, came out against the Senate blockade, but what choice had he? If the Grits corner the protectionist vote, NDP support collapses.) Many, especially in the latter camp, have had to reverse long- held positions on fundamental questions of political philosophy. But that is a trifle in Canadian politics.

CHANGING TACKS

Turner's own hypocrisy has been most widely celebrated. It was indeed but months ago that he was declaring that ''at the end of the day'' the will of the people's elected representatives must prevail. The Liberal leader has always made much show of love for the Commons and parliamentary tradition, yet now proposes that the senators, prominent among them those 11 whom he ''had no option'' but to appoint, should put off the end of day indefinitely.

There's nothing new in this. Since his return to public life, Turner has never shown the least inclination to prefer principle to politics. How he acquired such a reputation is hard to fathom; it seems to be based chiefly on his bumbling demeanor.

Whether running before the mob on the rights of francophones in Manitoba or of refugees off the East Coast, whether yielding to the demands of Pierre Trudeau as Prime Minister or of Herb Gray as opposition leader, whether changing tacks on free trade or federalism, Turner has always taken his name literally. The only issue on which he's been prepared to take an unpopular stand is his own leadership.

It is curiously revealing that Turner should appropriate Gary Hart's slogan of ''let the people decide.'' Both have shown the same arrogant contempt for the people in discussions of their own character. Both seem to feel the rules others must follow do not apply to them; and indeed, that they are called to judge others.

True, Mulroney has no mandate from the people to pursue free trade, just as the Liberals had no mandate to impose wage and price controls in 1975. But that is a matter for Mulroney's conscience and the judgment of history. Who appointed John Turner to decide what unadvertised legislation is important enough to warrant an election? Since when do opposition leaders set the voting date?

But for that matter, why should the government be allowed to? Turner's critics, while ceding the legality of his move, make much of constitutional convention. It's true that convention should not be made light of, but it's also true that some conventions we could well do without. It confers an unnecessary advantage on the government of the day to be able to call elections according to its own timetable, rather than, as in most civilized countries, on a fixed schedule. Mulroney, despite Turner's manoeuvres, still has 14 months of latitude to sail in: just as Turner could kill the trade deal any time after Jan. 1, so Mulroney could arrange a few months' extension without risk of annulment.

In any case, an election is not the proper means of resolving the matter. True democrats on both sides ought to be joining in the call for a referendum: a fair fight, without distraction of party, candidate or secondary issues, nor insult to the same. Since none of the major players has made any such call, none can pose as tribunes of democracy.

The whole affair, finally, points up the desperate need for Senate reform, but with the passage of Meech Lake - another initiative for which the Prime Minister had no mandate, though neither opposition leader seems to think that worth calling an election over - that is now impossible. The senators need never fear for their offices. Which perhaps explains van Roggen's bravery.