LONDON, NOV. 2 -- Sir Geoffrey Howe's resignation from Britain's Cabinet marks, in some important ways, a symbolic end to a remarkable era of political domination by Prime Minister Margaret Thatcher.

Thatcher has survived many crises and no one is writing her off this time. But the right-wing program of economic and political transformation known as Thatcherism, support for which has plunged in recent months, now appears to be a spent force.

Howe was not only the last surviving member of Thatcher's original 1979 Cabinet, but as her first chancellor of the exchequer was also the main architect of Thatcherism. He drew up much of the legislation that privatized Britain's bloated state companies and broke trade union power.

The immediate cause of his departure yesterday was a longstanding dispute over Britain's future role in Europe. But the effect has been to put Thatcher's own future in jeopardy and to raise anew within her own Conservative Party the question of whether, after 11 years in office, it is time for her to go.

"Mrs. Thatcher is a remarkable woman who has done remarkable things for this country," Anthony Marlow, a member of Parliament and an outspoken Conservative dissident, told BBC Radio. "In the 70s, she encapsulated the ambitions, the aspirations, the mood of the country. In the 80s she gave effect to them. What she's got to do is to assess whether she now in the 90s actually shares and understands the hopes and aspirations of the country . . . because the mood of the country has changed."

The quarrel over Europe -- with Thatcher taking a hard-line nationalist stance on economic and monetary union to Howe's more conciliatory and integrationist position -- has captured most of the headlines here. But many Britons have focused instead on a list of domestic issues on which Thatcher's government has stumbled badly and been forced into retreat.

Her moves to keep a tight lid on spending for schools in next year's budget were thwarted after her own education secretary, John MacGregor, publicly argued for more money while resisting her plan to implement a voucher scheme to allow parents and students more freedom of choice. He won on both issues.

Similarly, after an embarassing loss in a special election for a vacant parliamentary seat, Thatcher reversed herself by lifting a four-year freeze on family benefit payments.

That move was particularly revealing because the half-hearted way it was done alienated both supporters and opponents.

Rather than provide an across-the-board increase, Thatcher approved a one pound ($1.95) per-week boost for the eldest child in each family. It made little economic or social sense, critics said, and backfired politically as well.

"The lesson is: The longer you stay in the bunker, the more you get out of touch," said Michael White, political editor of the Guardian newspaper.

One by one, the politicians who helped Margaret Thatcher reshape the face of Britain in the 1980s have fallen aside, leaving her isolated and bereft of Cabinet colleagues who share her fervent ideological vision. The departure over the past year of chancellor of the exchequer Nigel Lawson, environment minister Nicholas Ridley and now Howe means she has lost all of the senior figures who until recently dominated her Cabinet.

The manner of their going has -- with the exception of political soulmate Ridley -- left a bitterness that damages her within her own party. Unlike in the United States, where presidential aides and Cabinet secretaries who quit under fire usually have to fall back on their memoirs to settle scores, British politicians return to the backbenches of Parliament, where they can enjoy a ready-made public forum and make life uncomfortable for a prime minister.

Lawson has taken several verbal shots at Thatcher's handling of the economy and Europe since his resignation a year ago. Howe can be expected to do the same. And Edward Heath, the former Conservative prime minister whom Thatcher bested for control of the party in 1975, has remained a constant critic, as he demonstrated again today.

"Instead of having a leader who holds the party together and goes to great lengths to do so, we have one who allows the party to break up," Heath told a radio interviewer.

The most prominent remaining members of her Cabinet -- Foreign Secretary Douglas Hurd, Chancellor of the Exchequer John Major, Environment Secretary Chris Patten and party chairman Kenneth Baker -- are neither loyalists nor ideological Thatcherites. They are moderate, pragmatic politicians who share Howe's viewpoint more than Thatcher's but who have decided, for the sake of the party or their own careers, to support the prime minister's bid for a fourth electoral victory.

The dominance of the moderates was enhanced today when Thatcher announced she was shifting MacGregor to the post of Leader of the House and Kenneth Clarke to education secretary and adding William Waldegrave, another pro-European Tory, to the Cabinet in Clarke's old job as health secretary.

The moderates may be having second thoughts about their support of Thatcher, especially after her emotional anti-European performance in Parliament earlier this week. Still, most analysts believe a serious leadership challenge within the party is unlikely in the next few weeks.

Howe has said he will not run against Thatcher, and so has Michael Heseltine, the Tory dissident who remains her main rival for power. They believe she still commands a majority of Conservative lawmakers, and few wish to see a bloody intraparty power struggle as a prelude to the next general election.

Instead, many expect Thatcher to enter the new year hobbled by the controversy over Europe and a growing economic recession, and facing another round of controversy over her new local tax system -- all while presiding over a political party at war with itself.

"The lid has come off," said Peter Temple-Morris, another Tory dissident in Parliament. "The strains that have obviously been on {Howe} and pushed him to the edge are on us as well."