WASHINGTON — The U.S. Department of Agriculture late Friday extended the period for exporting countries to ship tariff rate quota (T.R.Q.) sugar by one month to help ease the tight supply of sugar in the United States.

The U.S.D.A. said countries holding U.S. import quota for 2010-11 may ship sugar until Oct. 31, 2011, one month past the end of the current marketing year without having to pay additional duties.

“This action is expected to reduce the shortfall and provide additional flexibility for U.S. refiners,” the U.S.D.A. said.

About a month ago the U.S.D.A. said T.R.Q. imports for 2011-12 may enter the United States as of Sept. 1, 2011, a month ahead of the start of the new fiscal year, “in response to increased tightness in the U.S. raw cane sugar market.”