Author of The Worldly Philosophers, a 3-million-copy seller, Robert Heilbroner offers here a compendium of readings from the ''worldly philosophers'' themselves. The selections range from the earliest economic thought to such towering volumes as Adam Smith's The Wealth of Nations, Thomas Malthus's Essay on the Principle of Population, David Ricardo's Principles of Political Economy, and John Maynard Keynes's The General Theory of Employment, Interest, and Money. Acting as ''a docent, not merely an editor,'' he takes the reader through the core arguments with ''brilliantly clear commentary'' (New York Times Book Review).