She said the Obama administration is pressing for a greater understanding of the hostage-taking and rescue effort there that left three Americans dead.
Clinton parried tough questions from Republicans, offering a detailed timeline of events on Sept. 11 and the Obama administration efforts to aid the Americans in Libya while simultaneously dealing with protests in Cairo and other countries.
GOP lawmakers repeatedly questioned Clinton about whether she had seen earlier requests for beefed-up security.
"I did not see these requests. They did not come to me. I did not approve them. I did not deny them," she said.
She took House Republicans to task for recently stripping $1 billion in security aid from the hurricane relief bill and the Senate panel for failing for years to produce an authorization bill.
In something of a valedictory, Clinton noted her robust itinerary in four years and her work, nearly 1 million miles and 112 countries.
"My faith in our country and our future is stronger than ever. Every time that blue and white airplane carrying the words "United States of America" touches down in some far-off capital, I feel again the honor it is to represent the world's indispensable nation. And I am confident that, with your help, we will continue to keep the United States safe, strong, and exceptional."
Clinton is the sole witness at back-to-back hearings before the Senate and House foreign policy panels on the September raid.
Clinton had been scheduled to testify before Congress last month, but an illness, a concussion and a blood clot near her brain forced her to postpone her appearance.
Absent from the hearing was Sen. John Kerry, D-Mass., the man tapped to succeed Clinton. His swift Senate confirmation is widely expected, with his confirmation hearing scheduled for Thursday. Sen. Bob Menendez, D-N.J., the incoming chairman, presided over the hearing.
Clinton's testimony was focusing on the Libya attack after more than three months of Republican charges that the Obama administration ignored signs of a deteriorating security situation there and cast an act of terrorism as mere protests over an anti-Muslim video in the heat of a presidential election. Washington officials suspect that militants linked to al-Qaida carried out the attack.
Politics play an outsized role in any appearance by Clinton, who sought the Democratic presidential nomination in 2008 and is the subject of constant speculation about a possible bid in 2016. The former first lady and New York senator - a polarizing figure dogged by controversy - is about to end her four-year tenure at the State Department with high favorable ratings.
A poll early last month by the Pew Research Center for the People & the Press found 65 percent of Americans held a favorable impression of Clinton, compared with 29 percent unfavorable.
On the panel at the hearing were two possible 2016 Republican presidential candidates - Florida's Marco Rubio and Kentucky's Rand Paul, a new member of the committee.
Clinton did little to quiet the presidential chatter earlier this month when she returned to work at the State Department after her illness. On the subject of retirement, she said, "I don't know if that is a word I would use, but certainly stepping off the very fast track for a little while."
With respect to Benghazi, the review singled out the Bureau of Diplomatic Security and the Bureau of Near East Affairs, saying there appeared to be a lack of cooperation and confusion over protection at the mission in Benghazi. The report described a security vacuum in Libya after rebel forces toppled the decades-long regime of strongman Moammar Gadhafi.