THE POLITICAL TENSION in the European Common Market seems to be organizing itself along economic class lines. In everything budgetary, the Common Market is Robin Hood in reverse, taking from the poor and giving to the rich. Among the four large countries, the rich are France and Germany; the poor are Italy and Great Britain.

Since most of the Common Market budget consists of agricultural subsidies, the specific issues are exquisitely narrow. Are the French being fair about imports of lamb? What's to be done about those huge surpluses of dairy products? But since Western Europe's political system and its newly elected parliament are being tested on it, the main question is worth following even though you may not necessarily be deeply interested in the prices of butter and eggs in nine different currencies.

The agricultural subsidies were part of the original deal in which the Common Market was stitched together nearly a generation ago. The French were adamant about the protection of their peasants, a mainstay of successive conservative French governments. The Germans expected to pay most of the bills but, since they had peasants of their own, they accepted it. The subsidized products tend to be the northern ones -- grain, meat and milk. The subsidies don't reach Italy's fruit and vegetables. Now that Britain is in the market, with its efficient agriculture and its heavy food imports, its assessments are the highest of all.

While the Italians have been complaining about this pattern for years, they have never had quite the confidence or political presence to press their objections. But lack of self-confidence and political presence have never been British failings. Britain is now forcefully making its grievances known. That's what lay behind the bruising and indecisive meeting of the heads of the Common Market governments last week in Dublin.

The British would have to pay, under the present rules, a staggering $2 billion in Common Market contributions next year. Too much, said Britain's Prime Minister Margaret Thatcher. At length, the other members -- i.e., France and Germany -- grudgingly offered a $700 million reduction. Not enough, said Mrs. Thatcher. There everything remains, awkwardly, until another meeting in late winter. Mrs. Thatcher has wisely made it clear that Britain does not intend to drop out of the market. But, as the French demonstrated at one point in the mid-1960s, one recalcitrant member can paralyze the whole institution.

For Europeans, the case will be important as the first seriously divisive question put to the continent's new parliamentary democracy. For Americans, it is further notice that in basic economic matters -- which include, for example, oil -- the European community is not yet ready for common policy or common action.