MARGARET THATCHER has begun a battle for her political life. By next Tuesday, when a first ballot is cast in a contest for her party's leadership, Mrs. Thatcher will know whether or not her 11-year term as Britain's prime minister is over.
Even if she fends off a leadership challenge by Michael Heseltine, one of her former ministers, there is a broadening consensus that her days in 10 Downing Street may be numbered.
The crisis for the woman who took over the leadership of the Conservative Party in 1975 and rose to become the ``Iron Lady'' of British and international politics began to deepen on Nov. 1, when Sir Geoffrey Howe, deputy prime minister and a loyal lieutenant ever since Thatcher came to power, suddenly resigned from the government.
His departure was followed by a blistering resignation speech in the House of Commons, in which he assailed Thatcher for allegedly endangering Britain's interests by harboring ``nightmare visions'' of European countries ``undermining British democracy.''
Sir Geoffrey went on to attack Thatcher's abrasive leadership style, and called on Conservative members of Parliament (MPs) to consider whether they wished to go on serving under such a leader.
Coming from a politician famous for understatement and mild manners (an opponent once said that being attacked by Sir Geoffrey was like being savaged by a dead sheep), the speech was described by Peter Temple-Morris, a leading Conservative backbencher, as ``utterly devastating.''
The British news media took up the phrase and began measuring the damage Sir Geoffrey had done to the prime minister. But worse was to come for the woman who had sat aghast throughout the Howe onslaught and who, at the end of it, could only say that she ``regretted the manner'' of her deputy's resignation.
Mr. Heseltine, who stormed out of the Thatcher Cabinet four years ago after a disagreement with the prime minister about purchases of European defense equipment, took soundings among his fellow Conservative MPs who decide each year who is to lead their party.
Heseltine's soundings revealed that ``well over 100'' of the 374 Conservative MPs wanted him to lead the party, he said. On Wednesday, he threw his hat into the ring.
``Under my leadership the party could win the next general election. Under Mrs. Thatcher, it could not,'' he said.
The statement drew bitter attacks from Thatcher loyalists. Sir Marcus Fox, deputy chairman of his party's backbench committee, said he ``deplored'' a move that was ``unnecessary and can only damage the prime minister.''
Michael Mates, a former Army colonel who is the Heseltine campaign director, angrily rejected the attacks, claiming that Thatcher had herself had ``done damage enough'' and was no longer fit to lead Britain.
In the lobbies of the House of Commons, the turmoil unleashed by the Howe resignation and the Heseltine challenge promised to continue throughout the weekend and in the run-up to the first ballot in the leadership contest.
In theory, under Conservative Party rules, Heseltine needs 159 votes to keep Thatcher from winning on the first ballot. But Conservative MPs said yesterday that there were signs that many of their number, nonplused by the ferocity of the Howe attack and worried about signs that Thatcher might be losing her political grip, were planning to abstain. If there were 20 or 30 abstentions, Heseltine would be in striking distance of forcing a second ballot one week later.
And if that happened, Thatcher might either resign or decide to face a second contest in which other contenders would be likely to enter the race.
Other challengers could include Sir Geoffrey himself. Thatcher's own officials have raised the possibility that Douglas Hurd, the respected foreign secretary, might enter the lists.
A Heseltine loyalist said yesterday: ``We can wound her so severely that she would either have to step down or accept her fate as a lame duck leader. And our party does not like lame ducks in charge.''
Thatcher has ideas of her own. Immediately after Heseltine threw down the gauntlet, a Downing Street source said the prime minister was ``ready for battle.'' A majority of just one vote would be ``enough for the prime minister to continue.'' She expected to ``trounce'' Heseltine.
Independent-minded backbenchers trying to decide which way the tide was flowing appeared to feel that Thatcher was underestimating the extent of dissatisfaction with her leadership.
One pointed out that Sir Geoffrey's resignation had been preceded by that of Nigel Lawson, the former chancellor of the exchequer.
``Why can she not retain the loyalty of her lieutenants? Perhaps she has become too domineering,'' the MP said.
Another senior Conservative MP said this was ``the most serious blood-letting'' since Thatcher won the Conservative leadership from Edward Heath.
Heseltine said yesterday that he parted company from Thatcher on three key matters.
``Her attitudes to Europe antagonize our friends and, as Sir Geoffrey says, are harming the nation. Her style of government prevents the Cabinet from making collective decisions. And her introduction of the poll tax has caused profound concern to millions of people'' he said.
Heseltine's criticism of the poll tax struck a chord with many Conservative MPs, fearful that their parliamentary majorities will be eroded at the next general election by voters angry with what they see as an unfair fee.