A PLAINTIVE delegation of Republican governors went to call at the White House yesterday and urge President Reagan to cut down imports of automobiles. Six of those governors state their position in a letter that we publish today. They point out that Britain, Italy, France and Spain have already imposed quotas to hold off the competition from Japan. We would not have thought that the present state of ecomonic affairs in Britain, Italy, France and Spain was a terribly attractive argument in favor of imitating them.

But the governors are absolutely right in suggesting that protectionism is far stronger there than in this country. The United States, with the world's strongest ecomony, is the natural leader in trade policy. If the United States now abandons its position and puts quotas on Japanese cars, most of the European government will react with simple relief. They will rapidly put still more quotas on still more sectors of their own economies, citing the American policy as justification.

And against whose exports do you suppose those quotas will be directed? Japan's? Certainly, but not only Japan's. Above all they will be directed against American exporters who, contrary to the impression in this country, are seen in Europe as ruthlessly and relentlessly competitive. Western Europe is the country's biggest foreign market, and for every $2 worth of goods that Americans import from Europe they sell $3 worth there. Every government in Europe is under domestic pressure to do something, anything, about American exports. The only reason they don't succumb is that Washington would squawk. If Mr. Reagan does as the governors ask, he won't be in a position to do much squawking.

It's not a matter of what's good for Japan, or for France, but what's good for Wisconsin, Delaware and the rest. Before the governors carry their crusade any farther, there are a few questions that they ought to ask -- not here in Washington, but at home.

If Gov. du Pont knows anybody in the chemical industry, he might ask about the benefits of quotas to it. The United States exports more than twice as many dollars' worth of chemicals as it imports. The Europeans have been complaining bitterly about the rapacious and unfair competition they are suffering from cheap American exports of chemicals and symthetic fibers. Gov. du Pont wants to "conserve the core of our industrial system." Doesn't that include chemicals?

Gov. Dreyfus could usefully ask people in Milwaukee about the implications of a trade war for machine tools and computers.Most of the businessmen there know that American exports of all machinery -- including automobiles -- substantially outweigh the imports. One of the leading reasons for it is the advanced technology and managerial skill that has for generations been at home in Wisconsin. Gov. Orr and Gov. Thompson might talk to some of the farmers in their states about foreign trade. European restrictions on American farmers for years. They have leaned on the State Department heavily and fairly successfully to work down those quotas. To Mr. Orr and Mr. Thompson, Japanese cars and American soybeans might seem like two totally cases. But to the French minister of agriculture and the Common Market's agriculture commissioner, there are many thought-provoking and inviting parallels between them.

Gov. Milliken thinks of Michigan as a one-industry state, but of course it isn't. The governors speak movingly of the need to take a "humanitarian step" for the auto workers and their families. As the governors must know, the labor force in the auto industry faces a severe reduction in the 1980s regardless of trade policy. In the meantime, what about the industries with the capacity for strong export growth -- and how about a humanitarian regard for the people who work for them, and their families? How about the people who make computers, and aircraft, and digitally controlled machine tools -- not to mention the farmers?