NEW YORK (CNNMoney.com) - President Bush has nominated Steven Preston to head the Small Business Administration after Hector Barreto announced he was resigning to lead a Hispanic organization.

Preston will leave his post as executive vice president of the ServiceMaster company, a large franchise firm, to take over the SBA from Barreto, who will become national chairman of The Latino Coalition, an advocacy group based in Washington, D.C.

Barreto's leadership of the agency came under fire from key members of Congress, as well as Gulf Coast business and political leaders, who said the SBA was slow to provide help to businesses devastated by Hurricane Katrina last year.

Last month, in an interview with CNN, Barreto defended his performance and said he had no plans to leave the agency. His office said Tuesday that he was not pressured by the White House to step down.

But senior administration officials said complaints about the SBA were constant, including direct appeals to President Bush during his visits to the Gulf Coast, and when CNN reported on the controversy in early March several senior officials said they expected a change at the agency soon.

Barreto, in his letter of resignation to President Bush, said "It has been a unique honor to serve as Administrator of the U.S. Small Business Administration and to help execute your vision to bring unprecedented opportunities to all entrepreneurs in every community as they seek to realize their dreams. I am proud that the agency has delivered strong results and achieved historic milestones on behalf of a vital component of our great economy, America's small businesses."

Barreto has agreed to remain in his post as SBA administrator during a transition period. He has led the SBA since July 2001 and is the second longest serving administrator in the agency's 53-year history.

Preston's nomination requires Congressional approval.

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