WASHINGTON (CNN) -- Housing and Urban Development Secretary Alphonso Jackson resigned Monday, amid multiple ethics investigations and criticism from top lawmakers.

HUD Secretary Alphonso Jackson speaks at a news conference in December.

Jackson, who said his resignation would take effect April 18, did not mention the allegations in his brief statement Monday, saying only he needed to focus on "personal and family matters."

The resignation came after criticism from members of Congress that Jackson has refused to respond adequately to allegations of impropriety.

President Bush said in a statement, Jackson "made significant progress in transforming public housing, revitalizing and modernizing the Federal Housing Administration, increasing affordable housing, rebuilding the Gulf Coast, decreasing homelessness, and increasing minority homeownership." Watch Jackson talk about his career at HUD »

Sen. Chris Dodd, D-Connecticut, who recently called for Jackson to resign, welcomed his decision to step down.

"I hope this change in personnel will be matched by a change in policy that brings real solutions to the housing crisis that has triggered this economic recession," Dodd said.

No names have been floated as candidates to replace Jackson, a long-time friend of President Bush from their days in Texas.

One possibility would be to promote from within the department, given the short time remaining in the president's term and the hostility he faces from the Democratic-controlled Senate, which must confirm Jackson's replacement.

Dodd and Sen. Patty Murray, D-Washington, demanded Jackson's resignation 10 days ago, saying the ethics allegations have distracted from the secretary's ability to handle the nation's housing crisis.

"Secretary Jackson has repeatedly demonstrated that he is not in the position to provide the type of leadership that is necessary during these trying and difficult times," Dodd said in the statement. He said an inspector-general's report recently stated that Jackson had advised staffers to "take political affiliation into account in awarding contacts," and "serious allegations about his impropriety" are under investigation in three cases, although Dodd did not name them.

Dodd is chairman of the Senate Committee on Banking, Housing and Urban Affairs. Murray is chairwoman of the Senate Appropriations Subcommittee on Transportation, Housing and Urban Development.

Jackson has recently been accused in a lawsuit of retaliating against housing officials in Philadelphia, Pennsylvania, for blocking a land deal with one of Jackson's friends. The FBI has been investigating allegations that Jackson steered a federal contract to a golfing buddy based in South Carolina.

The secretary has denied wrongdoing and White House officials have said for months that the president still has confidence in Jackson. No charges have been filed against him.

Jackson has been a key player in the Bush administration's efforts to handle the national housing and mortgage crisis.

Before coming to Washington, Jackson ran Dallas' housing authority for seven years and then led a Texas power company. He also was head of the Federal Housing Administration. His announcement of his resignation comes four years to the day after he was confirmed as secretary.

Speaking to reporters at HUD headquarters in Washington on Monday, Jackson said he had devoted his career to improving housing opportunities.

"As the son of a lead smelter and nurse midwife, and the last of 12 children, never did I imagine I would serve America in such a way," Jackson said about his Cabinet post. "I am truly grateful for the opportunity."

"We have helped families keep their homes, we have transformed public housing, we have reduced chronic homelessness, and we have preserved affordable housing and increased minority homeownership," he said.

A Jackson adviser told CNN earlier that the secretary has been privately talking about resigning since late last year because he's grown weary over multiple ethics investigations and allegations that he cannot focus full time on the nation's housing crisis. E-mail to a friend

CNN's Ed Henry contributed to this report.

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