MARGARET Thatcher has served notice that she intends to throw her prestige and energies into a campaign against ``creeping federalism'' in the European Community. That decision promises to put her on a collision course with her successor as prime minister.
The former British prime minister will become president of the Bruges Group, an organization dedicated to opposing the economic and political union of the European Community (EC).
Mrs. Thatcher's 11-year term ended amid recriminations when the ruling Conservative Party replaced her with John Major. When she left 10 Downing Street seven weeks ago, she said, ``I shall go on fighting for everything I believe in.''
Thatcher's decision to accept the presidency of the Bruges Group has delighted defenders of British political sovereignty, who argue that European unity has already gone too far.
Its members include scores of senior parliamentarians - for example, Nicholas Ridley, who was forced to resign as a Cabinet minister last year after harsh comments about the Germans - and several prominent academics, including Norman Stone, professor of modern history at Oxford University.
The only other post Thatcher has accepted since she resigned is the presidency of the No Turning Back Group, consisting of Thatcherite members of Parliament.
Thatcher's friends say she is planning a series of major addresses this year, in Europe and North America, in which she will continue to argue the case against a single European currency and central bank.
Her speaking plans promise to coincide with the intergovernmental conferences at which the 12 EC states will be trying to achieve closer economic and political unity.
At the conferences, the Major government will attempt to distance itself from Thatcher's antifederalist views and to forge friendlier relations with other EC governments.
A senior Conservative who served in Thatcher's Cabinet but holds strong pro-European views said: ``This will make it harder for Mr. Major to develop a clear-cut European policy of his own. Mrs. Thatcher could divide her own party by opening up the very wound the new prime minister is attempting to heal.''
Norman Tebbit, a former Conservative Party chairman, ardent Thatcherite, and Bruges Group supporter, said the ex-prime minister was exercising her right of free speech and would not create problems for the government.
Edward Heath, a former British prime minister, disagreed. ``What Mrs. Thatcher wants is to break up the European Community,'' he said.
Patrick Robertson, director of the Bruges Group, said he was ``delighted'' by Thatcher's decision to assume leadership of the organization. A little ``hand-bagging'' by Thatcher would be a good thing.
Mr. Robertson said last weekend that he would urge her to undertake a ``global lecture tour'' on free markets and European integration. ``I would also like her to address a rally of the Bruges Group in the Free Trade Hall in Manchester,'' Robertson said. The Victorian-era hall is seen by opponents of European federalism as an historic symbol of free-trade ideas.
The Labour Party opposition received Thatcher's decision to lead the Bruges Group with considerable glee.
George Robertson, its foreign affairs spokesman, said: ``She has indicated that she is not content to be a backseat driver. She wants her hands on the steering wheel, and she's quite prepared to run Mr. Major into a bank on the side of the road.''
Among Conservatives, there are clear signs that the decision is already reviving a controversy on the European issue.
William Cash, a leading figure in the Bruges Group, welcomed it, and noted that Thatcher spoke with great authority on European questions.
Peter Temple-Morris, a senior Conservative backbencher, described the move as ``worrying, in that Europe has been a potentially divisive issue for the Conservative Party for some time.''
It is also, however, an issue which stirs deep convictions - and which is beginning to generate new lines of thought within the Conservative Party.
The Institute of Economic Affairs (IEA), a right-wing think tank that reflects the views of Thatcherite Conservatives, last week published a blueprint for constitutional change in the EC.
Frank Vibert, the IEA's deputy director, said the Rome Treaty (the EC's Constitution) should be revised to reduce the powers of the European Commission (the EC's executive arm), increase the powers of national parliaments, and make it easier for member governments to opt out of EC decisions they do not agree with.
Mr. Vibert said that at the intergovernmental conferences Britain should argue for a more decentralized EC.
The IEA blueprint reflects the thinking of the Bruges group. Vibert said it had already been circulated in British government departments, together with an annex suggesting the language in which key passages of the Rome Treaty could be rewritten.