An independent inquiry into the attack on the United States diplomatic mission in Libya that killed four Americans on Sept. 11 sharply criticizes the State Department for a lack of seasoned security personnel and relying on untested local militias to safeguard the compound, Congressional and State Department officials said Tuesday night.

The investigation into the attacks on the diplomatic mission and C.I.A. annex that killed Ambassador J. Christopher Stevens and three others also faulted State Department officials in Washington for ignoring requests from officials at the American Embassy in Tripoli for more guards and safety upgrades to the diplomatic mission.

The panel also blamed the State Department for waiting for specific warnings of imminent attacks to act rather than adapting security procedures and protocols to a deteriorating security environment. By this spring, Benghazi, a hotbed of militant activity in eastern Libya, had experienced a string of assassinations and attacks, including one on a British envoy’s motorcade.