NAIROBI, SEPT. 25 -- Somali militiamen shot down an American Black Hawk helicopter over Mogadishu early this morning, killing three U.S. crewmen on board and intensifying debate in Washington over the U.S. military presence in Somalia.

Three other American soldiers and three Pakistanis were wounded in a fierce gun battle that erupted as ground troops of the U.N. peace-keeping force in Somalia converged on the site where the helicopter crash-landed in flames, according to U.N. officials and news reports from Mogadishu. An unknown number of Somalis were killed in that battle, the reports said.

No one claimed responsibility for today's attack, which was one of the most dramatic in the escalating struggle for control of the capital's streets and marked the first time Somalis had downed a U.N. helicopter. But U.S. military officials blamed militiamen loyal to fugitive warlord Mohamed Farah Aideed, who is accused of staging bloody ambushes and mortar bombardments against U.S. troops and other U.N. peace keepers.

Today's attack came as the helicopter was patrolling an area near the abandoned presidential palace in a section of Mogadishu controlled by Aideed.

Military sources said the helicopter was struck by a rocket-propelled grenade and that the pilot was able to fly the burning craft away from Aideed's turf to a more secure area close to Mogadishu's port. The pilot and copilot, both of whom were injured in the attack, apparently determined that the other crew members were dead -- one was blown from the craft -- and they walked to a checkpoint manned by U.N. soldiers from the United Arab Emirates.

The charred wreckage of the helicopter was immediately surrounded by jubilant, dancing Somalis, according to foreign journalists in Mogadishu and their Somali staff members.

Somalis held up what they claimed were burned portions of the U.S. servicemen's bodies, but it could not be determined whether the bits of flesh and military clothing they displayed had come from the helicopter, which was reduced by fire to little more than a rotor and gutted shell, special correspondent Mark Huband reported from Mogadishu.

Somalis also were said to have gone to a hotel where the few foreign journalists in the capital stay, to show them an American soldier's belt and an identity card.

At one of Mogadishu's marketplaces, Somalis were said to have carried around a decapitated corpse in a food sack, saying it was the body of one of the helicopter crewmen and charging passersby to look at the remains, according to a report from Massimo Alberizzi, a reporter for the Italian newspaper Corriere della Sera who contributes to the Reuter news agency.

In Washington, Pentagon and State Department officials said they could not confirm the grisly reports. Officials in Washington and Mogadishu said it was unclear whether all of the crewmen's remains had been recovered, and a U.N. official told Huband that it was likely that some of the remains were in the Somalis' possession.

The attack appeared to mark a significant psychological victory for the guerrillas in an increasingly violent confrontation in Mogadishu. U.S. troops spearheading the U.N. search for Aideed have tried to operate primarily from the safety of the skies, but helicopters recently have been hit by gunfire and by shrapnel from grenades exploding nearby. Several American crewmen have been injured, but before today the guerrillas had never managed a direct hit.

U.S. Army Maj. David Stockwell, the chief U.N. military spokesman in Mogadishu, called the downing "a very lucky shot."

Fifty-six foreign troops -- including seven Americans -- have been killed in more than 3 1/2 months of street fighting in Mogadishu. More than 200 peace keepers have been injured, including scores of Americans who have been shot, hit by shrapnel or injured while running for cover during the near-nightly mortar and grenade attacks against U.S. and U.N. compounds and staging areas.

Concern is mounting in the United States that what began as a humanitarian mission with the deployment of U.S. troops to Somalia in December has become a military quagmire, and a growing number of voices are calling for the more than 5,000 American troops to be withdrawn. The Senate passed a nonbinding resolution calling on President Clinton to obtain congressional approval to keep the troops in Somalia past Nov. 15 and to outline a specific timetable for their withdrawal, and the House seems set to follow suit.

Since inheriting the Somali mission from the Bush administration, Clinton's policy makers have made intervention there a symbol of commitment to peace keeping in Africa and around the world. They warn that if driven out of Somalia by gunmen, peace-keeping operations elsewhere, including Angola and Mozambique, could be endangered.

The Clinton administration today reiterated its goals of protecting food aid deliveries and restoring order in Somalia. White House Press Secretary Dee Dee Myers said today's attack "underscores the need to reestablish security in Mogadishu to prevent the international humanitarian efforts from being undermined."

"Somalia is on the road to recovery," she said. "We must not allow this substantial yet fragile progress to be threatened by the brutality of warlords who would profit from the suffering of others and thwart the will of the overwhelming majority of Somalis who seek peace and reconcilation."

But the chairman of the Senate Appropriations Committee, Robert C. Byrd (D-W.Va.), said that "having completed the original mission to feed the starving people of Somalia, we should bring our military forces home."

"Without a legitimate purpose, we will be drawn further into this quagmire, with a very real prospect for the continued loss of American lives," Byrd said in a statement.

Clinton is scheduled to meet with U.N. Secretary General Boutros Boutros-Ghali on Monday, and Somalia will be a main topic in discussions about international peace keeping.

For the proponents of continued tough U.N. military action against Aideed, the timing of today's attack could not have been worse, coming just four days after the arrest of Osman Ato, Aideed's right-hand man and chief financer. U.S. and U.N. officials asserted that they had turned a significant corner in the conflict; Stockwell called the arrest a "milestone."

But today's events showed that even after Ato's arrest, the gunmen can continue to fight and inflict casualties, despite U.S. officials' insistence that the ranks of Aideed's militia have been depleted and that its morale is low.

Because of concern that U.S. citizens might be taken hostage by Aideed loyalists and held in exchange for Ato -- or for Aideed, if he is apprehended -- American journalists have left Mogadishu.

Staff writer Daniel Williams in Washington contributed to this report.