The landmark trade agreement signed recently by the United States and Canada is fresh evidence that bilateral negotiation to remove protectionist barriers can and must be the cornerstone of an effective American trade policy.

The treaty confirms something else -- that the Establishment game on trade, as played by editorial writers and Wall Street, by most Republicans and too many Democrats, is a loser. The Establishment attitude on trade is that we have to write off whole industries -- that our people can't compete anymore -- and that we must lower American wages through foreign competition.

On this issue and many others, the Establishment is separated from the consequences of its own opinions. The tough decisions will not be tough on any of the editorial writers who advocate them, the publishers who print them or the corporate presidents who applaud them. Unfair trade practices do not lower the standard of living of economists; and the editorial board of The Washington Post does not have to worry about its jobs being shipped abroad.

I reject the idea that somehow Americans are incapable of efficiently producing steel or cars, televisions or VCRs -- that we must accept an economy that swaps $15 for $5-an-hour jobs.

I reject the excuse that we are only yielding old enterprises for new ones. In fact, because of unfair trade practices, we are already losing the industries of the future. An Apple computer that costs $1,500 here costs $3,000 in Japan. And no matter how hard Americans work, no one's going to buy a computer for twice what it's worth.

And I reject the rationalization that unfair trade practices are the price we pay to export our agricultural abundance. The Europeans keep out most of our farm products. In Japan a pound of American beef sells for $30, and our apples would cost $5 each, except that Japan won't let us sell them there at all.

So I'm tired of hearing all the blame for the trade deficit put on our workers and farmers when they're victimized by decades of myopic management and anachronistic government policies. And I'm tired of the self-serving tactic of labeling as ''protectionist'' any measure to defend ourselves from foreign trade practices that raise impassable barriers to our exports.

In repeated editorial assaults against the Gephardt Amendment, The Post suggests that the choice we face is between another Smoot-Hawley tariff and more one-way free trade. The real issue is whether America will negotiate seriously for equal terms of trade, and that is what my policy is all about.

We demand such a balance in arms control; why not in the economic arrangements that are the essence of our strength? Why should trade be the only place where we bargain with nothing to back us up? You can't blame other countries for taking maximum economic advantage -- for entering our market and closing theirs -- when we will not even exert minimum economic leverage.

In the few cases where we have, we have made real gains -- and the record plainly refutes those who oppose the Gephardt Amendment and suggest instead that we rely on the generosity of our trading partners.

When President Reagan, pushed by a bipartisan Congress, imposed sanctions on Japan in response to that nation's assault on American semiconductors, The Post warned of a trade war -- but Japan backed down.

When we refused Canadian demands for unequal advantages and were ready to let our mutual trade agreement expire, The Post was aghast -- but Canada yielded and signed an agreement that truly does open up markets on both sides of the border.

Indeed, history shows that when America pressures other nations to remove barriers, barriers come down because other nations will not risk losing access to the most valuable market in the world. But it's naive to expect them to open up without incentive.

This administration usually resists that approach, turning to it only as a last resort when the political heat is high. Instead it has pursued the latest Establishment remedy, which is to devalue the dollar to the level of a Third World currency.

''Just wait 'til the dollar drops,'' the editorials promised, ''and the trade deficit will fall.'' But it doesn't matter how cheap you make American goods if foreign barriers keep them out or reinflate their cost. And now a devalued dollar threatens to bring on higher interest rates and then a new recession.

I am a Democrat who is proud to protect American workers and American jobs, not by closing down our markets but by insisting that other countries open theirs.

When we try to ship an American car to a country such as Korea, the government there slaps on a 50 percent customs tax, an 80 percent excise tax, a 60 percent defense tax -- nine separate tariffs in all. And when that government is done, a $10,000 Chrysler K-car costs $48,000 in Korea.

The Gephardt Amendment requires one thing: negotiation to remove unfair barriers such as those Korean taxes (countries like Hong Kong with huge surpluses but an open market are unaffected), and it gives the president the option of taking action only if negotiation fails.

I know the reaction of the Establishment -- of apostles of the status quo -- and of Democrats who would prefer to talk only a little and do even less in areas like trade. But in all conscience, the Democratic Party cannot play the Establishment game. We are not the party of conventional wisdom, we are the party of change. At our best, we have never won the support of the Establishment. Most editorial writers fervently denounced Franklin Roosevelt and the New Deal; tax reform was opposed by the strongest corporate lobby in history.

So the central challenge facing Democrats in 1988 is to break with the Establishment view and stop the export of employment, the sell-off of farms and the demise of America's heartland. If we don't do this, who will?

The writer, a Democratic representative from Missouri, is seeking his party's presidential nomination.