* Illness interrupts her final weeks as U.S. top diplomat
* Two deputies to testify on Benghazi findings in her place
* High popularity fuels speculation on 2016 aspirations
By Andrew Quinn
WASHINGTON, Dec 15 (Reuters) - Secretary of State Hillary Clinton, who canceled an overseas trip last weekend because of illness, suffered a concussion after fainting due to dehydration, prompting the postponement of her scheduled congressional testimony on the attack on a U.S. mission in Libya, officials said on Saturday.
"While suffering from a stomach virus, Secretary Clinton became dehydrated and fainted, sustaining a concussion," State Department spokesman Philippe Reines said in a statement.
"She has been recovering at home and will continue to be monitored regularly by her doctors," Reines said, adding that she would work from home and stay in regular contact with other top officials.
Clinton, 65, fell ill with a stomach virus last weekend and was forced to cancel a planned trip to the Middle East and North Africa. The virus also hit other members of her staff, who were returning with her from a European trip, and was described as uncomfortable, but not medically serious.
Clinton's doctors, Lisa Bardack of the Mt. Kisco Medical Group and Gigi El-Bayoumi of George Washington University, issued a statement saying that Clinton fainted as a result of "extreme dehydration" due to the virus.
"Over the course of this week we evaluated her and ultimately determined she had also sustained a concussion," the doctors said in their statement, which was distributed by the State Department.
"We recommended that the secretary continue to rest and avoid any strenuous activity, and strongly advised her to cancel all work events for the coming week. We will continue to monitor her progress as she makes a full recovery."
Clinton has often been cited as a potential Democratic candidate for the U.S. presidency in 2016 and frequently refers to her general good health. She said in an interview with ABC broadcast on Wednesday that she has "incredible stamina and energy."
She has maintained a punishing schedule in her final weeks as the top U.S. diplomat, a position she intends to leave toward the end of January when U.S. President Barack Obama is sworn in for a second term.
Obama telephoned Clinton to wish her well, White House spokesman Tommy Vietor said.
Clinton had been expected to testify on Dec. 20 before the House of Representatives and Senate foreign affairs committees on a report on the deadly attack on the U.S. diplomatic post in Benghazi, Libya, in September that killed the U.S. ambassador and three other Americans and raised questions about security at far-flung posts..
Jodi Seth, a spokeswoman for Senate Foreign Relations Committee head John Kerry, said that given her condition, Clinton's testimony would be postponed, but did not say until when. Seth said the planned hearings would be held with other senior officials appearing in Clinton's place.
The Republican chair of the House of Representatives Foreign Affairs Committee, Ileana Ros-Lehtinen, issued a statement saying she was sorry to hear of Clinton's ill health, but it was "unfortunate" she would be unable to testify before the committee next week.
"We still don't have information from the Obama Administration on what went so tragically wrong in Benghazi that resulted in the deaths of four patriotic Americans," Ros-Lehtinen said.
"We have been combing through classified and unclassified documents and have tough questions about State Department threat assessments and decision-making on Benghazi. This requires a public appearance by the Secretary of State herself."
Ros-Lehtinen's statement said William Burns and Thomas Nides, deputy secretaries of state, would provide testimony in Clinton's place.
Republicans have criticized the Democratic Obama administration for its early public explanations of the attack.
Much of the criticism focused on U.S. Ambassador to the United Nations Susan Rice, who on Thursday said she was withdrawing her name from consideration to replace Clinton as secretary of state to avoid a potentially disruptive confirmation process.
Clinton has appointed a special panel known as an accountability review board to assess both the Benghazi incident and the official response to it.
The board's report, which will contain both classified and unclassified sections, is expected to be complete next week and Clinton has promised to be as transparent as possible with Congress in sharing its findings.
Clinton, whose husband, Bill Clinton, was president from 1993 to 2001 and who herself came tantalizingly close to winning the Democratic presidential nomination four years ago, has used her star power to promote U.S. interests around the world since Obama named her to lead the State Department in 2009.
She has consistently been rated as the most popular member of Obama's Cabinet, leading to speculation she might mount another White House bid in 2016, although she herself has played down suggestions that she still hopes to become president.
"I've said I really don't believe that that's something I will do again. I am so grateful I had the experience of doing it before," Clinton told ABC's Barbara Walters in the interview broadcast on Wednesday.
"I just want to see what else is out there. I've been doing ... this incredibly important and ... satisfying work here in Washington, as I say, for 20 years. I want to get out and spend some time looking at what else I can do to contribute."