NAIROBI, AUG. 4 -- An internal report by the United Nations' legal office in Somalia has sharply criticized the July 12 American-led helicopter attack on a Somali leader's compound, saying the world body has a "moral" and "legal" obligation not to kill people -- even in Somalia's combat-like conditions -- before offering them a chance to surrender.

The three-page report focused on a U.N. attack by U.S. Cobra gunships that fired antitank missiles and cannons into a strategy meeting of key advisers to fugitive militia leader Mohamed Farah Aideed in Mogadishu, the Somali capital. Several of Aideed's commanders were killed in the raid, which U.N. officials said was timed to wipe out a "key terrorist cell" plotting ambush attacks against U.N. peace keepers, including Americans, in Somalia.

The U.N. envoy in the war-torn country, Jonathan Howe, said last month that the attack was "well planned" for the time the meeting was taking place.

But the report, prepared by the U.N. Justice Division in Somalia the day after the helicopter assault, raised what it called "important legal and human rights issues" about the attack. It asked whether the United Nations should target individuals and "whether the {United Nations} should hold itself to a higher standard of conduct" in what originally was a humanitarian mission to protect food supplies in Somalia.

"We believe as a matter of policy, short prior notice of a destruction of a building with humans inside must be given," the report stated. "From the legal, moral and human rights perspective, we counsel against conducting military operations that give no notice of attack to occupants of buildings."

The unsigned report was said to have been written by Ann Wright, who until a few days ago was the United Nations' top justice official in Somalia, responsible for helping rebuild the shattered nation's police force and judicial system. Wright left at the end of her contract to return to the United States.

The report, considered sensitive within the U.N. bureaucracy, was given to The Washington Post by U.N. employees who said they have grown disillusioned with the course of the world body's military campaign against Aideed and his militia.

Disenchantment over the direction of the Somalia operation and mounting civilian casualties there is known to be widespread within the U.N. staff. This feeling has been particularly strong among workers in the humanitarian section of the United Nations who believe the military has subordinated their aid efforts in its six-week hunt for Aideed. Howe ordered the militia leader arrested for his suspected role in the killings of U.N. peace keepers. The report is likely to keep alive the debate over the U.N. methods and practices in Somalia's ongoing guerrilla war.

Since the July 12 helicopter assault, the United Nations has largely halted its offensive against Aideed, even though officials insist they are still tracking his movements. U.N. and Clinton administration officials say that for the moment, the United Nations lacks the manpower in Somalia to try to retake the streets of Mogadishu from Aideed's gunmen, who have veritable free run of most of the southern half of the divided capital.

The lull in U.N. military actions in Mogadishu also is attributed to sensitivity within the world body to the outcry after the helicopter attack. Criticism mounted from Somalis, from relief agencies and from within the United Nations, where many charged that the assault was an unnecessary provocation and turned the world body into another belligerent faction in Somalia's civil war.

The U.N. report said the operation in Somalia was "applying military methods traditionally found in declared war/combat areas without a U.N. declaration of war/combat."

It said the assault created "unnecessary hostility" that "dramatically" increased the danger to relief workers and foreign journalists in the capital.