* Lawmakers want answers on envoy's death, security
* Probing possible collusion between attackers, guards
By Susan Cornwell and Mark Hosenball
WASHINGTON, Sept 20 (Reuters) - Secretary of State Hillary Clinton said on Thursday she was forming a panel to investigate the attack on the U.S. Consulate in Benghazi, Libya, that killed Ambassador Christopher Stevens and three other U.S. officials.
The panel, whose creation is generally required by law when someone is killed or seriously injured at a U.S. mission abroad, will be chaired by Thomas Pickering, a retired diplomat who served as U.S. ambassador to Russia, India, Israel, Nigeria, El Salvador, Jordan and at the U.S. Mission to the United Nations.
Such panels, made up of four people chosen by the secretary of state and one by the U.S. intelligence community, are charged with writing a report on whether security systems and procedures were adequate, and they might recommend improvements.
Lawmakers have demanded answers on how Stevens, a State Department information management officer and two security agents could have died in the incident, a n d whether sufficient security was in place. Stevens' death marked the first time a U.S. ambassador had been killed in such an attack since 1979.
The panel's inquiry is separate from an FBI probe of the Benghazi attack.
U.S. authorities are investigating possible collusion between the militants who launched the attack and locally hired Libyan personnel guarding the facility, three U.S. officials said on condition of anonymity.
So far, there is no proof the attackers were helped by Libyan security personnel hired by the consulate. One official said the Obama administration was playing down that possibility.
But all the officials said the question of whether the attackers had inside help was a serious issue in the U.S. investigation into the attack, which occurred on the 11th anniversary of the Sept. 11 attacks on the United States.
Clinton gave lawmakers a classified briefing in an effort to answer questions and make the case for continued U.S. engagement in the Middle East despite a wave of anti-American protests in the region this month.
U.S. embassies in Egypt, Sudan, Tunisia and Yemen have been attacked and U.S. diplomatic facilities in the Middle East and North Africa have been the target of protests sparked by a film made in California that depicts the Prophet Mohammad as a womanizer and a fool.
Appearing at a forum sponsored by Univision and Facebook, and hosted by the University of Miami in Coral Gables, Florida, President Barack Obama said the United States would not retreat from the region.
"My message to the presidents of Egypt, Libya, Tunisia and these other countries: we want to be a partner with you, we will work with you and we stand on the side of democracy," he said.
"But democracy is not just an election, it's also are you looking out for minority rights, are you respecting freedom of speech, are you treating women fairly?" he added.
"The one thing we can't do is withdraw from the region. The United States continues to be the one indispensable nation."
Speaking at a news conference before she briefed U.S. lawmakers, Clinton also stressed the importance of U.S. relations with such countries despite questions about whether the United States should continue aid following the protests.
"We are concerned, first and foremost, with our own people and facilities, but we are concerned about the internal security in these countries because ultimately that puts at risk the men, women and children of these societies on a daily, ongoing basis if actions are not taken to try to restore security," she added.
A congressional committee wrote to Clinton on Thursday demanding information about the attack in Benghazi, including all U.S. security analyses and threat assessments before the violence and any documents that clarify whether the attack was spontaneous or premeditated.
"The American people have a right to know the facts about this egregious attack on U.S. sovereign territory," Republican Representative Jason Chaffetz wrote to Clinton, setting an Oct. 4 deadline for her to provide the information.
Adam Smith, the senior Democrat on the House Armed Services Committee, attended part of the briefing and said - as Reuters reported on Wednesday - that the U.S. ambassador to Libya had five security guards with him. Smith said he thought that was an appropriate number.
Asked about possible collusion between Libyans working for the U.S. Consulate in Benghazi and the attackers, Smith said, "There is no evidence of that at this time."