WASHINGTON — In a letter earlier this week 13 U.S. senators urged U.S. Department of Agriculture Secretary Tom Vilsack to increase tariff rate quotas (T.R.Q.) for raw and refined sugar to relieve tight U.S. sugar supplies.

"A confluence of factors, including production shortfalls, strong demand and the continued closure of a major domestic refinery following a tragic accident last year, have contributed to a tight U.S. sugar market," the March 23 letter said. "By increasing current sugar T.R.Q.s for raw and refined sugar, U.S.D.A. can help ensure that confectioners, bakers, ice cream makers and other U.S. food producers have access to an adequate supply of sugar at a reasonable cost."

The T.R.Q.s, or import quotas, were set in September 2008 for the 2008-09 (October-September) sugar marketing year. At that time the U.S.D.A. said the domestic market likely would need additional sugar supply. In its March World Agricultural Supply and Demand Estimates, the U.S.D.A. projected a sugar stocks-to-use ratio of 9% on Sept. 30, 2009, historically low compared with a typical ratio near 15%.

"We hope that the Department will review current market conditions and make appropriate adjustments to ensure an adequate supply of sugar for the domestic market," the senators said.

Signing the letter were Senators Dick Durbin of Illinois, Sam Brownback of Kansas, Herb Kohl of Wisconsin, Dick Lugar of Indiana, George Voinovich of Ohio, Lamar Alexander of Tennessee, Arlen Specter of Pennsylvania, Roland Burris of Illinois, John Ensign of Nevada, Bob Casey of Pennsylvania, Judd Gregg of New Hampshire, Christopher Bond of Missouri and Russ Feingold of Wisconsin.

"The letter demonstrates strong bipartisan support for taking steps to ensure that the U.S. sugar market remains adequately supplied," said Fred Hensler, chairman of the Sweetener Users Association (S.U.A.). "The sweetener user, consumer and trade communities are appreciative of the support from members on this important issue."

The S.U.A. added, "Because of the lead time to purchase, ship and refine raw sugar, a T.R.Q. increase must occur in the very near future in order to avoid supply disruptions later this year." The S.U.A. estimated an additional 750,000 tons of sugar was needed this year.

Domestic sugar producers noted that although domestic sugar supply will be short of projected demand, large shipments from Mexico have filled the void so far. Mexican sugar may enter the United States unrestricted under the North American Free Trade Agreement. In similar situations in the past, producers have indicated such requests for increased imports were more a matter of domestic users not wanting to pay current prices than of actual shortages. Most U.S. sugar producers have indicated they still have supply available for 2008-09.

As of March 11 the U.S.D.A. projected 2008-09 total sugar supply at 11,821,000 tons, raw value, consisting of 1,660,000 tons carried over from the previous year, 7,630,000 tons of domestic beet and cane sugar production and 2,531,000 tons of imports. Total sugar use for the year was projected at 10,840,000 tons, with an ending balance of 981,000 tons on Sept. 30, 2009.

Under current legislation, the U.S.D.A. which administers the U.S. sugar program, could not adjust T.R.Q. levels until April 1.