LONDON, NOV. 19 -- Margaret Thatcher's campaign to remain leader of the ruling Conservative Party and prime minister of Britain became highly personal today as Thatcher accused challenger Michael Heseltine of being a closet leftist and asserted that deposing her from office now "would be the cruelest thing."

After several days of passive campaigning in which she generally relied on surrogates to speak on her behalf, Thatcher came out with guns blazing in an interview with the Times of London and in an article published under her name in the Daily Telegraph.

Times editor Simon Jenkins said "she poured out a truly Wagnerian fury at the timing and content" of Heseltine's challenge, accusing her former defense secretary of advocating socialist-style "corporatism" and "interventionism" that she said was "akin to some of the Labor Party policies."

"Look, you've seen the crumbling of the more extreme forms of that philosophy in the Soviet Union," said Thatcher, an ardent free marketeer who is generally to the right of her opponent on economic issues. She said a Heseltine premiership would "jeopardize all I have struggled to achieve."

A combative Thatcher told reporters at the Paris summit of the 34-nation Conference on Security and Cooperation in Europe, "It's not time to write memoirs yet. . . . I most earnestly believe that we shall be in No. 10 Downing Street at the end of this week -- and a little bit longer than that."

Analysts said Thatcher's aggressive stance reflected fears among her advisers that Heseltine may do better than they expected in the first round of voting on Tuesday for the post of party leader and prime minister. The vote is by secret ballot of the 372 Conservative members of the House of Commons.

Some analysts detected similar fears behind Thatcher's call for a referendum on whether Britain should in effect scrap sterling and adopt a single European currency. Heseltine, who wants to move ahead much faster with European political and monetary union than does the prime minister, rejected the idea.

Heseltine's cause has been helped in recent days by a series of opinion polls indicating that as prime minister he could erase the opposition Labor Party's double-digit lead in voter preference polls and help the Tories squeak through to victory in the next general election.

Heseltine, who has sought to play down personal issues in a whirlwind five-day campaign, expressed surprise over Thatcher's accusations. He noted that as her first environment secretary, he engineered the first big privatization of her administration -- the selling off of thousands of public housing units to their occupants -- and had sharply cut back staff at both the environment department and later at the ministry of defense.

"Nobody said that I was an interventionist or corporatist then; they thought I was doing exactly what the Tory Party is all about," Heseltine told the British Broadcasting Corp.

He hammered away at the theme of electability and said the so-called poll tax, Thatcher's highly unpopular new system of local taxation, had caused the party "a great deal of embarrassment. . . . It is important to deal with that issue before we lose a general election."

Thatcher, who has held office since 1979 and won three straight national elections, is expected to outpoll Heseltine in Tuesday's contest. But she needs to win not only an outright majority of the 372 voters, but also win 15 percent more votes than the challenger to avoid a second ballot a week later.

In the Times interview, Thatcher poured scorn on the claim that she was an overbearing, divisive figure whose time had come and gone. "You would never have had any of the great philosophies or religions if you had gone out and said, 'Brothers, I believe in consensus.' Never. Consensus is a form of words you use when you cannot get agreement."

Thatcher also charged that there was an element of male chauvinism in criticisms of her style. "Had I faltered or taken some of the easy short-term ways out, we would have neither the success nor the international reputation we have. Yet when a woman is strong, she is strident. If a man is strong, gosh, he's a good guy."