WASHINGTON — The stunning collapse of Iraq’s army in a string of cities across the north reflects poor leadership, declining troop morale, broken equipment and a sharp decline in training since the last American advisers left the country in 2011, American military and intelligence officials said Thursday.

Four of Iraq’s 14 army divisions virtually abandoned their posts, stripped off their uniforms and fled when confronted in cities such as Mosul and Tikrit by militant groups, principally fighters aligned with the radical Islamic State in Iraq and Syria, or ISIS, the officials said.

The divisions that collapsed were said to be made up of Sunni, Shiite and Kurdish troops. Other units made up of mainly Shiite troops and stationed closer to Baghdad, the Iraqi capital, were believed to be more loyal to the government of Prime Minister Nuri Kamal al-Maliki, a Shiite, and would most likely put up greater resistance, according to the officials.

Still, Lt. Gen. John N. Bednarek, who heads the office of security cooperation at the United States Embassy in Baghdad, said at a closed hearing of the Senate Armed Services Committee that some of the Iraqi soldiers who guarded the Green Zone in the capital had come to work wearing civilian clothes under their military uniform, according to one senator. The implication was that the troops were prepared to strip to civilian attire and flee if they came under heavy attack.