As S.B.A. administrator, he was responsible for revamping the government’s Disaster Assistance Program, which was still reeling from the Gulf Coast hurricanes of 2005 when he arrived. He was also responsible for supporting the nation’s small businesses with an $80 billion portfolio of direct and guaranteed business loans, venture capital investments and disaster loans.

Earlier this year, Mr. Preston was sharply criticized when Democrats in Congress learned that his agency had given a $1.2 million contract to a former Bush administration official who lacked experience in helping small businesses compete for government contracts.

The contract went to the VBP Group, a company based in Paradise Valley, Ariz. The company’s owner, Vernon B. Parker, served as assistant secretary for civil rights in the Agriculture Department from April 2003 to January 2006.

Mr. Preston called on the agency’s inspector general to investigate.

“Based on the information provided by your staff, and some research conducted by my staff, I believe there is sufficient cause for concern over the events surrounding this contractor,” Mr. Preston wrote to Nydia Velázquez, the New York Democrat who is chairwoman of the committee.

Mr. Jackson, 64, prided himself on working to keep vulnerable families in their homes, to revitalize public housing and to preserve affordable housing as head of the $37 billion housing department.

But Mr. Jackson began stirring controversy soon after he was named housing secretary.

In 2004, less than two months after his confirmation, Mr. Jackson told a House panel that he believed poverty “is a state of mind, not a condition,” provoking strong criticism. Two years later, he said in a speech that he had canceled a contract for a company after its president told him that he did not like Mr. Bush. Mr. Jackson later said he had made the story up.

In March, Mr. Jackson took a pounding from senators who demanded that he respond to accusations that he had steered hundreds of thousands of dollars to friends for work at the Virgin Islands housing authority and the reconstruction in New Orleans after Hurricane Katrina. Senior Democrats called on him to resign.