AT THE LEAST, the Japanese government miscalculated the political message that it seemed to deliver with its announcement on automobile exports to the United States. It was an uncharacteristically inept move. Over the coming year, Japan said, it will limit the number of cars shipped here to 2.3 million -- a larger quota, but still a quota. That decision arrived at a moment in which the two governments were locked in negotiations over sales of American telecommunications equipment to Japan.

When the Reagan administration dropped its insistence on import quotas for Japanese cars, it was inviting the Japanese companies to compete here without further restraint. In return it wanted Japan to give American companies equal access to their market, beginning in a visible and important field -- telecommunications -- in which the Americans are genuinely ahead of the competition.

The White House took the Japanese response last week to mean that Japan would rather stick with quotas on cars -- and, by implication, also to stick with the buy-Japanese rule that generally prevails in telecommunications. In an unusually sharp statement, the White House immediately told the Japanese that it was no deal and that the United States will continue to insist on Ameri- can manufacturers' rights to sell communications products in Japan free of the traditional discrimination.

Perhaps the White House is wrong and the explanation is simpler -- that Japan only feared a great surge of Japanese cars into the United States, inviting a protectionist reaction in Congress. The quotas in effect for the past four years -- legally imposed by Japan, in fact demanded by the United States -- have heavily favored three of the Japanese automobile companies. There are five or six others that want largershares of the market, and perhaps the Japanese government felt that it could not control the scramble without formal quotas.

But the quotas are a fundamentally bad idea. Over the past four years they have clearly pushed up the prices of both domestic and imported cars in this country. Similarly, Japan would serve its people's interests by opening up its own markets. Rather than holding down the numbers of cars shipped to this country, they would do better to sell as many as they can -- but see to it that those sales are balanced by growing sales of American goods to Japanese customers. The place to begin would be, clearly, telecommunications.