Washington ? Seven American soldiers were killed and 11 were wounded Monday when two U.S. helicopters took enemy fire during the most deadly allied air and ground offensive of the war in Afghanistan.

The U.S. assault, code-named Operation Anaconda, marked a new approach. Instead of relying on Afghan forces to take the fight to the al-Qaida, with U.S. troops in support, the Americans took the lead. Afghan, Canadian, Australian, German, Danish, Norwegian and French forces were supporting.

In all, 40 U.S. soldiers were wounded since the operation began Friday.

Fighting was fierce, by all accounts, in difficult conditions.

U.S. ground troops and pilots were operating at elevations between 8,000 and 11,000 feet, said Defense Secretary Donald H. Rumsfeld, cold, icy and snowy “like the Rocky Mountains in the middle of the winter.”

Army officials said Apache attack helicopters had been hit with extraordinary amounts of small arms fire but were able to continue their assaults. Air Force AC-130 gunships, armed with howitzers and 40mm cannon, were serving as the ground troops’ airborne artillery.

Air Force bombers and Navy and Air Force strike aircraft had dropped more than 350 bombs by Monday.

The men killed Monday were not the first U.S. casualties in the new offensive, which appeared far from finished. Army Chief Warrant Officer Stanley Harriman, 34, of Wade, N.C., was killed in a ground attack Saturday shortly after American forces, joined by Afghan and other allied troops, began the offensive against hundreds of fighters of the al-Qaida terror network and the former ruling Taliban militia dug in near the town of Gardez.

Differing accounts

Details on the two helicopter incidents were sketchy, and military officials offered two differing accounts of what happened.

“The fog of war will persist” until more of the soldiers involved are brought back and debriefed, Army Gen. Tommy Franks, commander of U.S. Central Command, told a news conference in Tampa, Fla., where he is based.

Pentagon officials said that in the first incident, an MH-47 Chinook helicopter ferrying a reconnaissance force to the area came under fire as it approached its landing zone. It landed under control, but when it lifted off, a soldier fell out of the aircraft. Franks said the crew did not realize it had lost him until it had left.

More than three hours later and about four miles away, Pentagon officials said, another MH-47 Chinook brought in troops to fight the al-Qaida forces. The helicopter came under machine gun and rocket-propelled grenade fire and was forced to make what Franks called a “controlled” crash landing.

The soldiers aboard the helicopter immediately came under fire and left the chopper to return fire, Pentagon officials said. Six were killed. Franks was unsure whether the casualties were sustained in the landing, the firefight or a combination of the two.

However, a Central Command spokesman, Marine Maj. Ralph Mills, said the first helicopter was flying low when it was hit with a rocket-propelled grenade that knocked a soldier out of the aircraft and caused a hydraulic problem. The first helicopter landed about a half-mile away, Mills said.

He said the second helicopter was flying in tandem with the first and rescued the downed crew, then returned to the area where the soldier fell out. The second helicopter dropped troops in that area, and six were killed in a firefight, Mills said.

The second helicopter returned and picked up the dead and wounded, he said. He said the wounded were being treated in a hospital in Afghanistan.

Franks said he watched the subsequent rescue operation that he watched unfold from his Tampa headquarters by video link.

Well-organized resistance

Rumsfeld said about half of the 40 soldiers wounded in the operation so far had returned to battle.

Names of the Americans killed Monday were being withheld until relatives could be notified.

The American deaths underscored not only the dangers in pursuing President Bush’s declared goal of eliminating Osama bin Laden’s al-Qaida but also the difficulty of assaulting what Pentagon officials say are well-armed and well-organized pockets of al-Qaida resistance in eastern Afghanistan.

The operation is being led by Maj. Gen. Franklin Hagenbeck, commanding general of the Army’s 10th Mountain Division.

Franks said the U.S.-led offensive was planned for several weeks and had as its objective a 60-square-mile area south of Gardez. He said about 1,000 Afghan troops were serving as a blocking force on the perimeter of the area to hem in the enemy and prevent large numbers from escaping.

Franks estimated that 100 to 200 enemy fighters had been killed and a small number taken as “detainees.” He said they included al-Qaida fighters, Taliban militia and Chechen and Uzbek fighters.

“We intend to continue to the operation until those al-Qaida and Taliban who remain are either surrendered or killed. The choice is theirs,” Rumsfeld told a Pentagon news conference.

General: No underestimation

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, disputed suggestions that the U.S. force, which numbered 800 to 900 men and included Army special forces soldiers and members of the 101st Airborne and 10th Mountain divisions, had underestimated al-Qaida resistance. He and Rumsfeld spoke confidently of winning the battle.

“When we began this operation, we knew that the al-Qaida and their supporters there would have two choices: to run or stay and fight,” Myers said. “It seems they have chosen to stay and to fight to the last, and we hope to accommodate them.”

Rumsfeld stressed that the battle probably would continue for some days, and he did not rule out sending in reinforcements.

He said several Afghan allied troops had been killed in the offensive but offered no specific number. He said enemy forces sustained “much larger” losses.

The death toll Monday represented the largest U.S. loss from a single battle in Afghanistan, where the fighting began Oct. 7. There have been several accidental crashes of other craft, including one in which seven Marines were killed when a refueling plane crashed in Pakistan.