AT a time when every public policy, however slight or sweeping, seems to excite passionate yeas and nays, post-war monetary policy inspires nothing but criticism.  The exasperation among the nation’s leading macroeconomists is palpable: On the left, Robert Solow pronounces modern monetary policy “mindless”; on the right, William Poole insists it “cannot be defended”; and in the center, Martin Feldstein calls the Federal Reserve’s record one of general “mismanagement” in behalf of which, Robert Gordon adds, “almost nothing can be said.”