With the strange crack-up of Liberal Canada now under way, he is more convinced than ever of the inevitability of his vision. Perhaps not this election, he cautions, but before long we, too, shall taste the fruits the two-party system has yielded the electors of Britain, the U.S., and British Columbia.

One cannot quarrel with the former political science professor's longing for a more polarized political culture. Infection with a little ideological extremism is the best thing that could happen to Canadian democracy. Ideology has here been supplanted by partisanship: in no country is the party line more strictly whipped, yet in no country do the parties stand for so little.

This sort of ideological sterilization by partisan identification is reinforced in the media. In most countries, public debate on the issues of the day is the task of champions, at least nominally nonpartisan, of warring philosophies of government. The typical Canadian political debate, as might be found on Gzowski, or Canada AM, or the op-ed page of the Toronto Sunday Star, involves a panel of three party hacks, who furiously slang one another in partisan terms, while agreeing on all the issues that count.

TOO MUCH CONSENSUS

This smothering consensus is the source of immense self-satisfaction among Canadian political elites - naturally enough. Consensus politics neatly excludes those tiresome masses from the debate. Without explicit doctrinal differences between the parties, the voter is reduced to a selection of managers, and the empty, squalid ideology of pragmatism emerges as the unchallenged public ideal. Disputes over principle there may be, but we rarely get to hear about them. All of which ensures that in Canada, there is no dogma like pragma.

So Broadbent's obsession is not to be discarded because it threatens the pax moderata. It is rather his fixation on the number two that is worrisome. In the first place, the tendency of two-party systems is not ordinarily to division, but consensus again. It was four decades of ''Butskellism'' consensus, after all, that the Thatcher revolution overturned in Britain.

But he's pointed in the wrong direction in any case. Canada's problem is not too many parties, it's too few. The very worst thing we could do is to settle ever more rigidly into the tribal politics of ''left'' and ''right.''

Again, the problem is not ideology per se, it is the narrowing of ideological debate to two more-or-less accidentally arranged bundles of ideas. This constricts thought, and distorts debate: good policies are rejected, and bad policies accepted, more for the company they keep than their separate merits.

There are an infinite number of different ways in which political ideas may be bundled, many of which would hang together with far more logic than the present choices. And there is considerable evidence that the electorate presents a far more complicated array of ideological tastes than the simplistic left-right spectrum would allow.

If this is so, why is this diversity not reflected in political representation? Why do we see only two or three parties in Canada? Because of our electoral system of ''first-past-the-post'' voting, in which the winner of a majority in any constituency takes all, leaving the minority unrepresented. This gives irresistible advantage to a small number of large parties, the one whose policies are least objectionable to the largest number being the winner.

It's very like the problem of ''market failure'' that afflicts broadcast television: though a minority might be strongly inclined to watch Shakespeare, the majority who don't mind having Dallas on while they do the ironing are the only ones whose choices count. In most markets, by contrast, minority tastes are fully represented, no matter how obscure, so long as the consumer is willing to pay the price.

The way to correct for the ''political failure'' of our present democracy is to restructure the system in such a way as to imitate the economic democracy of the market. That system is proportional representation, in which the number of seats each party is allotted is more closely tied to its share of the popular vote. I'll discuss some of the pros and cons of ''rep. by prop.'' next week.