By John S. McClenahen Productivity in America's factories increased at a seasonally adjusted annual rate of 4.6% during the third quarter of this year, three-tenths of a percentage point more than the 4.3% that the U.S. Labor Department initially reported last month. Productivity among durable goods manufacturers grew at a 4.8% rate during the July-to-September quarter while productivity advanced at a 5.4% rate among makers of nondurable goods, according to data the department released on Dec. 7. Hourly compensation among manufacturing workers rose 4.6% during the third quarter while unit labor costs were unchanged. In the larger nonfarm business sector of the U.S. economy, the third-quarter productivity growth rate was revised downward to 1.8% from its earlier 1.9% as hours worked increased more than did output. Economists generally had expected an upward revision to 2%.