THURSDAY BRITAIN voted for change on a scale greater than any in its political life for nearly a generation. Margaret Thatcher and her Conservative Party have won a victory that is solid and convincing. Ever since the late 1950s, the differences between the British parties have been rather narrow. Mrs. Thatcher rose to the top of her party by challenging that established consensus; and the country, hearing her message, has now made her prime minister. In office, no doubt, she will become less strident and didactic than she seemed in the campaign. But neither is there any doubt that people knew what they were voting for.

There was only one issue, and it began with the unions. It rests on a subtle question of minority and majority rights in an industrial democracy. By tradition and present law, a small minority of workers can pull a factory, and even an entire industry, to a halt until its grievance is dealt with. There are a lot of grievances these days, since the outgoing Labor government's successful campaign against inflation inevitably reduced the earnings of a lot of people. That was the reason for the surge of strikes that began last fall. Mrs. Thatcher intends to curtail the strikes by changing Britian's labor laws. She risks the same kind of militant reaction and industrial chaos that rapidly destroyed the last Conservative government five years ago. But she thinks that a majority of the country will support her-and the election returns suggest that she's right.

The issue was also the balance between incentives and security in an economy with ferociously steep income taxes and extensive social benefits. Mrs. Thatcher said that there had been too much emphasis on benefits for everybody, and not enough on rewards for the most productive and competitive. That, she believes, is the reason why Britian, by every economic measure, has fallen far behind France and Germany.

Over the past decade, industrial wages throughout Northern Europe have risen into the same range as in the United States, and in several European countries they are higher. In Britian, industrial wages remain about half the American level. Mrs. Thatcher draws support from British concern over this precipitate decline in relative national wealth, and in the political power and prestige that come with it.

Mrs. Thatcher's hard-line views on dealing with the Soviet Union and, even more, her unconcealed favor for the newly elected Muzorewa government in Zimbabwe-Rhodesia will raise some interesting questions for British relations with the United States and its other allies. But it is the attempt to change the country's basic social order that will make this government most interesting, and conceivably even historic. Countries usually attempt that painful feat only involuntarily, in times of great crisis. There is no crisis in Britian today, and yet there is a clear inclination to experiment with radical reform. It isn't fear or want that has brought Mrs. Thatcher to power, but rather a rising sense of national exasperation.