WASHINGTON (Reuters) - Mississippi Senator Thad Cochran claimed the role of Republican leader on the Senate Agriculture Committee on Thursday, giving the U.S. cotton-and-rice-growing region a more powerful voice in the debate over how to reform farm subsidies.

Cochran, who chaired the committee from 2003 to 2007, displaced Pat Roberts from Kansas, one of the largest wheat-growing states.

Roberts was an advocate of replacing traditional crop subsidies with a program that shielded crop revenue from poor yields or low prices.

Although the Senate passed new farm legislation in June, its $500 billion bill died in the House of Representatives, partly due to opposition from Southern growers. They wanted higher price supports and said the insurance-like system proposed in the Senate bill was not suited to rice and peanut crops.

In a statement, Roberts said Cochran asserted his seniority as a longer-serving member of the Agriculture Committee to take the post of ranking Republican. Roberts held the job for the past two years.

Following election to the Senate in 1978, Cochran, a lawyer by training, concentrated on government funding issues and eventually became chairman of the Senate Appropriations Committee in 2005, overseeing all federal spending.

(Reporting by Charles Abbott; Editing by David Gregorio)