BRITAIN'S NEW prime minister, John Major, is his Conservative Party's answer to a delicate question. The Conservatives (or most of them, at any rate) continue to cherish many of Margaret Thatcher's ideas, but they knew that she herself had become deeply unpopular. Prime minister since 1979, like many people long in power she had become increasingly peremptory, remote and dictatorial. With her in office, the party was clearly going to lose the next election. The solution has been to replace Mrs. Thatcher with her choice and protege, Mr. Major. So far the operation has been a success. The opposition Labor Party's long lead in the polls has already evaporated.

Mr. Major is a highly interesting figure -- less for his ideas, which are not yet fully known, than for his background and what it represents. One of Mrs. Thatcher's most remarkable achievements was to shift the balance in the Conservative Party sharply in favor of the rising middle class. Early in her tenure she ran an explicit campaign against a large category of eminent Conservatives, well-born and well-heeled, whom she considered intellectually lazy and much too inclined to go with the prevailing flow -- the "wets," as she and her followers derided them. A grocer's daughter who had made her way through Oxford, she knew a lot about the snobberies of British life by the time she became head of the party and had many scores to settle.

Mr. Major, a high school dropout who is the son of a circus performer, personifies a certain attitude toward inherited social class. He is interesting for another reason as well, his age. At 47, he will be the first prime minister in nearly 80 years to have no memory of either of the great wars in which his country was fighting for its life. World War II, with the incessant bombing of the cities, was the common experience that bound together the last generation of the British people, producing the powerful sense of community and the hunger for security that created the welfare state. But to most voters today the war is remote history, and it's now the very different tensions of a peaceful but highly competitive Europe that are changing British politics.

The Conservatives' opposition is in trouble. The traditional left, like the militant labor unions, is in decline because the industrial working class is shrinking. The future majorities lie in the various gradations of the middle classes -- but a party like the pre-Thatcher Conservatives, led by an established upper class, was not well equipped to capture them. Deep social change brought Mrs. Thatcher to power, and in choosing her successor she has tried to see to it that there will be no backsliding in her party.