* Closed door testimony expected to begin on Wednesday
* Top Clinton deputies to brief lawmakers on Thursday
* Political fallout has already taken a toll
Secretary of State Hillary Clinton on Monday received an official review of the September attack on a U.S. diplomatic mission in Benghazi, Libya, setting the stage for testimony on an incident that prompted a political furor and sharp questions about security at U.S. diplomatic facilities overseas.
The State Department said Clinton - who is convalescing after suffering a concussion last week - received the report from the Accountability Review Board formed to probe the attack which killed U.S. Ambassador Christopher Stevens and three other Americans.
"The ARB has completed its work. Its report has gone to the secretary this morning. She now has it," State Department spokeswoman Victoria Nuland said.
The committee has been meeting in private and State Department officials have declined to discuss almost all specifics of the Benghazi attack pending its reports.
The findings are expected to cover questions on whether enough attention was given to potential threats and how Washington responded to security requests from U.S. diplomats in Libya.
A determination that top State Department officials turned down those requests, as Republican congressional investigators allege, could refuel criticism of the officials - and possibly even end the careers of some of them.
Clinton had been expected to testify to Congress on Dec. 20 on the report's results, but is under doctors' orders to remain at home this week.
Deputy Secretary William Burns and Deputy Secretary Thomas Nides will testify in her stead at Thursday's open hearings of the Senate and House foreign affairs committees, Nuland said.
Prior to that, the Accountability Review Board's two leaders - retired Ambassador Thomas Pickering and retired chairman of the U.S. Joint Chiefs of Staff Michael Mullen - will testify in closed door hearings of the two committees on Wednesday, she said.
The political uproar over the Sept. 11 Benghazi attack has already claimed one victim.
U.S. Ambassador to the United Nations Susan Rice, widely tipped as a front-runner to replace Clinton when she steps down as secretary of state early next year, last week withdrew her name from consideration, saying she wished to avoid a potentially disruptive Senate confirmation process.
Republican lawmakers had blasted Rice for televised comments she made in the aftermath of the attack in which she said preliminary information suggested the assault was the result of protests over an anti-Muslim video made in California rather than a premeditated strike.
Rice has said she was relying on talking points drawn up by U.S. intelligence officials.
Nuland said the final report could contain both classified and unclassified sections, and that only the latter would be made publicly available.
Central questions raised include why the ambassador was in such an unstable part of Libya on the anniversary of the Sept. 11, 2001, attacks on New York and the Pentagon.
The five-person independent board usually includes retired ambassadors, a former CIA officer and a member of the private sector. It has the power to issue subpoenas, and members are required to have appropriate security clearances to review classified information.
Nuland said that Clinton - who intends to step down toward the end of January when President Barack Obama is sworn in for his second term - was "on the mend" following her concussion, which occurred when she fell as a result of dehydration due to a stomach virus.
She added that Clinton remained open to discussing the attack with lawmakers herself next month.
"She looks forward to continuing to engage with them in January and she will be open to whatever they consider appropriate in that regard," Nuland said.