Aug. 4 (Bloomberg) -- The Reuters/Jefferies CRB Commodity Index headed for its biggest one-day decline since March, led by plunging prices for natural gas, sugar and cocoa.

The CRB Index of 19 commodities fell 12.46, or 3 percent, to 403.56 at 11:52 a.m. in New York, the lowest since May 2. A settlement at that level would mark the biggest drop since March 19. The CRB slid 10 percent in July, the most in any month since March 1980, when the U.S. economy was in a recession.

Natural gas was today's biggest loser, dropping as much as 8.2 percent to a six-month low. Cocoa fell as much as 7 percent and sugar was down as much as 6.2 percent.

For related news: Energy markets: NRGMARKET BN <GO> Metal markets: NI METMARKET BN <GO> Currency markets: NI FX BN <GO>

Last Updated: August 4, 2008 11:55 EDT