London — Margaret Thatcher is having to devise a political strategy for the next two years that will somehow transcend her government's most serious failure so far: its inability to get a grip on inexorably rising unemployment.
Within weeks of the British ''political season'' when the major parties gather for their annual conferences, Mrs. Thatcher has received gloomy news. A record total of 3.3 million Britons are out of work - and the trend is still upward.
The latest statistics come at a time when other indicators seem to favor the government and its urgent attempts to prepare for a general election that could be called within a year. Inflation is on the way down, with financial analysts predicting that a rate of 9 percent may be possible next year.
At the same time bank interest rates have been falling, answering one of the main pleas of hard-pressed industrialists: that they be allowed to borrow more cheaply for expansion.
But the new unemployment figures have put a damper on the government's rising hopes. They mean that one person in seven of the available workforce is out of a job.
Mrs. Thatcher's employment secretary, Norman Tebbit, has spoken of a plateau being reached, but other political leaders, inside and outside the government, are not so sure.
The implications for Mrs. Thatcher are uncomfortable. In Britain's industrial north, unemployment is running as high as 16 percent, making it even harder for the government to mount a confident political campaign there.
Prime Minister Thatcher displayed cool nerves under the hail of political criticism that descended on her following release of the new jobless figure. Much of the criticism came from the Trades Union Congress, which will kick off the political season early next month.
The government is already locked in a 16-week struggle with health service workers determined to break beyond official pay guidelines. The prime minister has ordered her ministers not to give way under the pressure.
To some extent Mrs. Thatcher is still benefiting from the ''Falklands factor'' - the political advantage she gained over her opponents by her firm handling of the crisis in the South Atlantic. But the personal popularity built up then has begun to crumble around the edges.
Her aides are telling her that, despite unemployment figures described by critics as ''horrifying'' and ''terrible,'' she cannot order any significant U-turn in economic policy.
Some of her toughest advisers, including Mr. Tebbit, are telling her a margin of unemployment is necessary for monetarist policies to produce falling inflation and interest rates. But the inexorable broadening of the margin cannot be disguised, and there is talk at Westminster of the so-called ''wets'' in her Cabinet trying to stage a policy revolt in the autumn, in much the same way they did last year.
Thatcher aides say that even if there is a revolt the prime minister will have little trouble quelling it. She is in unquestioned control of the Conservative Party and can point out that the Labour opposition under Michael Foot is in disarray.
Labour's public squabbling means that it is alienating many voters who might otherwise cast their votes against the government at a general election.
The general secretary of the TUC, Len Murray, greeted the new jobless figures with an unusually detailed public statement on what he called an alternative economic strategy. The government, he said, should begin pumping money into the public sector to create jobs and turn back the unemployment tide.
But Mr. Murray later conceded that the government was most unlikely to heed his advice.
A nagging problem for Mrs. Thatcher is the gloomy mood of British industrialists. Sir Terence Beckett, the leader of the Confederation of British Industry (CBI), underlined the discontent of many members by holding detailed talks with the Labour Party's shadow spokesman on finance, Peter Shore.
The move was heavily criticized by some CBI members, and one major company quit the organization in protest. But most members were behind Beckett, some interpreting it as a subtle way of putting pressure on Mrs. Thatcher to do more to lift British industry out of its present deep recession.