By Susan Cornwell
WASHINGTON (Reuters) - Hillary Clinton is willing to testify once before a special congressional panel investigating the 2012 attack on U.S. diplomatic facilities in Benghazi, Libya, not twice as the panel's chairman has asked, her lawyer said on Monday.
The attack has hounded former Secretary of State Clinton for years, and Republicans in charge of the House of Representatives investigative panel are digging deeper as she ramps up her bid for the 2016 Democratic presidential nomination.
South Carolina Republican Trey Gowdy, chairman of the committee, said last month he wanted Clinton to answer questions at two public hearings about Benghazi and her use of a private email server while Secretary of State from 2009 to 2013.
Clinton's lawyer David Kendall said that there was "no basis, logic or precedent for such an unusual request."
In a letter to Gowdy, Kendall said Clinton was fully prepared to stay as long as necessary to answer all questions from the committee whenever she appears, but that she would not testify on two separate occasions "when one will suffice".
Four Americans including U.S. Ambassador Chris Stevens were killed when militants stormed U.S. facilities in the eastern Libyan city of Benghazi on the night of Sept. 11, 2012.
Gowdy's select committee was established last year to investigate the attack, despite numerous other probes by congressional panels and the State Department.
The earlier panels issued findings that generally criticized the State Department for not having adequate security at the U.S. compound in Benghazi, but concluded that the Obama administration's response to the attack was proper.
Republicans say more inquiry is needed because Clinton's State Department failed to protect diplomatic personnel.
Democrats say the panel is politically motivated and that Republicans are dragging out proceedings to undercut Clinton's candidacy.
Kendall said Clinton has already testified for more than five hours before other congressional committees on Benghazi.
Kendall's letter was released by the office of Representative Elijah Cummings, the senior Democrat on the Benghazi committee.
A spokesman for Gowdy said the chairman would take Kendall's response into consideration and issue a statement "regarding the path forward."
(Reporting by Susan Cornwell; Editing by Kevin Drawbaugh and Grant McCool)