LONDON -- The morning after Margaret Thatcher won another lease of up to five years on the Downing Street house she has inhabited for eight years, a wit wondered, ''After 13 years in No. 10, does she get the right to buy?'' That is a resonant question about the woman who, as the scourge of socialism, has required local authorities to sell municipal housing to occupants.

As the dust settles from her most recent dustup with the Labor Party, the electoral result stands revealed as a large event in the history of a large development in the late 20th century: the death of socialism.

In 1983, Labor failed to unseat a Conservative government that had presided over an economic contraction sharper than that of 1929. In 1983, and now again, Labor has failed to translate 3 million unemployed into a winning issue. Thatcher does well with skilled workers, the Alliance (Liberals and Social Democrats) does well with the intelligentsia (known here, delightfully, as the chattering classes).

In London this year, Labor did even worse than in 1983, when Thatcher had the Falklands factor and Labor was saddled with the inexpressibly unconvincing leadership of Michael Foot. This month Labor lost three working-class seats in London, including the seat held years ago by Clement Atlee, leader of the postwar Labor government. That is what happens when you raise property taxes 62 percent to hire an army of homosexual-rights and race-relations bureaucrats.

When a party plunges into steep decline, even its victories injure it. About one-quarter of the seats Labor won June 11 are now held by freshman MPs, many of them from the hard left. Already their voices are raised to blame the party's trouncing on insufficient commitment to ''real'' socialism. The Tories must be tempted to permit the televising of Parliament, the better to give the hard left ample exposure.

Some British socialists say socialism should not be judged by its works but by the purity of its ideals. But the central ideal is as implausible as the works have been disappointing.

Socialism is, as the saying goes, ''about equality.'' It carries the heavy baggage of having to believe that wealth and opportunity should be allocated somewhat coercively, to minimize the influence of talent. Socialism's implausible theory is matched by failures of practice. The collective purchase of ''key goods,'' such as housing, and public ownership of the ''commanding heights'' of the economy have lost whatever allure they once had.

In the 1950s and 1960s, British socialism tried to turn itself inside out by becoming more meritocratic than capitalism. It stressed ''planning,'' which meant: economic decision-making should be concentrated in a government composed of the best and brightest, so that reason could replace inefficient motives (''greed'') in animating the economy. But the lesson of planning is that the risk-averse bureaucracies are unsatisfactory sources of economic dynamism.

Elsewhere in Europe, there has been an ''Americanization of the left,'' the identification of the left with middle-class, often noneconomic, issues such as environmentalism, racial and sexual discrimination and opposition to nuclear weapons and power. But in Britain, the left, once an example of merely arrested development, has been regressing.

George Watson of St. John's College, Cambridge, notes that for the first time in this century it is trendy to be Tory. As for socialism, ''It has come down in the world, and top people have deserted it. It now belongs, if anywhere, to a world of the semi-literate and the semi-educated: to South American priests dedicated to new-fangled liberation theology, to tribal oligarchies in black Africa, and in Europe to the dropouts of higher education -- a sort of Lumpenpolytechnik of bedsitter Trotskyites to whom mid-Victorian concepts of class and consciousness still look like the latest thing.''

For the first time since Disraeli, Watson says, British conservatism is ideologically fervid, confident not just that conservatism is good for the stock market but that it is true. The embodiment of this confidence is the woman who, if her current government runs a full five years, at the next election would be younger than Churchill was when he first became prime minister.

The day after her third victory, she was asked if she would be prime minister in the year 2000, when she will be 75. ''You never know,'' she said. ''I might be here; I might be twanging a harp.'' As long as there are socialists to defeat, heaven can wait.