Libyan Fighters Repelled in Attack on Tripoli Hotel BENGHAZI, Libya - Libyan militia fighters assaulted a hotel in Tripoli housing members of the newly elected General National Congress on Tuesday, dramatizing the challenge the government faces in enforcing its ultimatum that all unauthorized brigades must submit to its authority or disband by the start of the day. The attack came as an American team arrived in Tripoli to investigate the death of Ambassador J. Christopher Stevens in an assault this month on the American Mission in Benghazi. Libyans who had spoken with the team said the investigators had reached Tripoli, but it was unclear when they might proceed to Benghazi, where security for American government officials is precarious. Representatives of the State and Justice Departments would not comment on the investigators" whereabouts. Although behind locked gates, the mission in Benghazi was all but unguarded on Tuesday. For two days after the attack, it had been completely open to looters and the curious, raising questions about the state of any evidence the investigators might find. The ambassador's death has brought on a new sense of crisis about the autonomous militias that have controlled Libya's streets since the collapse of Col. Muammar el-Qaddafi's police state. Shocked by the death and exasperated at the lawlessness, tens of thousands of civilians marched through the streets of Benghazi last Friday to demand more control of the militias, eventually storming at least four barracks and forcing the fighters to scatter. Some militia leaders in Benghazi said Tuesday that the new government led by President Mohamed al-Magariaf was trying to appoint its own officers over, or at least along with, the commanders of the three biggest brigades in the country's eastern region. Since Colonel Qaddafi's ouster, the brigades have acted as the government's main military and police force in the region, and two of them battled the fighters who attacked the United States Mission. The government considers all three brigades as "authorized" and, in fact, essential. But they remain independent, and last Friday one of the three came under attack by anti-militia demonstrators. If successful, the appointment of army officers to lead the militias could be the first tangible step toward government control of the brigades. Until now the transitional government has in effect handed army or internal security uniforms to brigade fighters and left their commanders in place. But brigade leaders gave conflicting reports of the new officers" authority. The commander of the Rafallah al-Sehati Brigade, Mohamed al-Gharabi, said in an interview on Tuesday that he had stepped aside to make room for the appointment by the army chief of Col. Salah bin Omran to lead his militia. Asked what his position was, Mr. Gharabi said, "Nothing." A spokesman for a coalition of brigades that includes Rafallah al-Sehati and others reported to be under a newly appointed commander said that their former leaders remained in place but that a new administrative officer had been added. "The commander of the brigade is still the same," said the spokesman, Ramiz Daghman, disputing Mr. Gharabi's account. A senior officer in Rafallah al-Sehati, Ismail al-Sallabi, also indicated that he expected his militia to resume its role without any such changes. "We feel hurt, we feel underappreciated," he said, describing his brigade's role in guarding ballot boxes and otherwise keeping the peace during the election in July. Security officials at the Tripoli hotel attacked by militiamen said that two people had been injured in an exchange of gunfire but that the hotel guards had repelled the attack. Two security officials at the hotel, the Rixos, said the attack grew out of a protest by three different groups of Libyan fighters, each with its own complaints. One group, based in the Souk al-Juma district, was angry over what it called a lack of government support when it fought suspected Qaddafi loyalists in the western town of Birak. Another group, based in Misurata, was angry over the death in Paris of a rebel fighter from that coastal city, Omran Shaaban, who was famous for a leading role in the capture and killing of Colonel Qaddafi. They believe Mr. Shaaban had died of injuries sustained at the hands of Qaddafi loyalists in the town of Bani Walid, a last bastion of Qaddafi support that remains outside the new government's control. Misurata and Bani Walid have a history of animosity dating to the Italian occupation decades ago. The third group may have been pushing back at the government's drive to rein in the militia, or perhaps just defending the Islamist militias that have come under increased pressure recently after a hard-line brigade was seen at the forefront of the attack on the United States Mission in Benghazi. This group chanted, "There is no god but God, and Abu Shagour is the enemy of God," against the new prime minister, Mustafa Abu Shagour, according to two hotel security officials. Suliman Ali Zwai contributed reporting from Benghazi.