Friedrich A. von Hayek, winner of the Nobel Memorial Prize in Economic Science, says that on the whole he approves of the economic policy of the Reagan Administration.Yet, when he discusses particulars, Professor von Hayek - a conservative who is best known as an unrelenting opponent of Socialism and lesser forms of economic interventionism -sounds less than approving. He applauds the determination in Washington and London to stop inflation but laments that both Governments seek gradual progress. "You have to do it rapidly and drastically," he says.