Britain locks horns with Europe. Common Market summit will focus on Thatcher's demand for a new deal

All eyes will be on British Prime Minister Margaret Thatcher at the ''make or break'' summit of the European Community in Brussels today and tomorrow. Will she be seen as the farsighted reformer of the world's largest trading group? Or will she come across as a modern-day version of a warlike Queen Boadicea? (It was Boadicea who around 60 A.D. unleashed her fury on her Roman invaders because of the unfair treatment her countrymen were receiving at the hands of their European overlords.)

Many Europeans recognize Mrs. Thatcher's complaint about unfair treatment. Britain pays into the EC far more than it gets back. But Mrs. Thatcher's confrontational style has tended to make Europeans more antagonistic than sympathetic to the British cause.

The other net contributor is West Germany, which has also been pushing for a cut in its contribution. But its objections have been more muted than those of Britain.

The EC is meeting in an atmosphere of crisis. Not only must the summit save it from bankruptcy, but it must try to satisfy Britain's demands for a fairer budget deal.

Britain, which pays 22 percent of the Community budget and only gets 13 percent back in return, insists that either it should pay in less or, alternatively, get more back. But on philosophical grounds, too, Britain strenuously objects to bailing out a financially squeezed organization which indulges in ''runaway'' surpluses and ''runaway'' spending.

Mrs. Thatcher won't be satisfied with stopgap measures that will merely tide the EC over its present crisis. She wants nothing less than an entire overhaul of the organization for, as she is fond of saying, ''I don't want to paper over the cracks. I want to get rid of the cracks.''

British preoccupations with ''fairness and discipline'' have so irked Europeans that Mrs. Thatcher's objections have become labeled ''the British problem.''

The British insist that Mrs. Thatcher is concerned about the welfare of the Community as a whole. British sources take some pride in believing that Britain provided the catalyst for change in the Community. They point to a general recognition within the Community that there should be budget balance and discipline.

Here in London, diplomatic sources feel the need to overhaul the basis on which member contributions are made will become more imperative in 1986. That is when Portugal is expected to join the EC. When it does, under the present budget arrangement, Portugal as the EC's poorest member will actually pay money to Denmark, one of the wealthiest in per-capita terms.