GARDEZ, Afghanistan, March 7 — Troop trucks, tanks and artillery from around Afghanistan began pouring into this provincial capital today as the U.S.-led military coalition strengthened its Afghan forces for what it hopes could be a final assault on al Qaeda and Taliban positions as early as this weekend.

While U.S. warplanes stepped up bombing runs over the mountains around the village of Shahikot, 20 miles southwest of Gardez, Afghan leaders began moving an additional 1,000 soldiers from other parts of the country to double the Afghan forces among the allied troops arrayed against enemy positions. The reinforcements arrived soon after the United States dispatched more attack helicopters to the area.

"This is war. We have decided not to come back until we have won," Abdul Mateen Hassan Khel, an Afghan commander who has contributed fighters to the U.S.-led coalition, said in an interview. "We believe this is the last war in Afghanistan."

The additional Afghan fighters were called in after U.S. commanders realized they had significantly underestimated the size and firepower of the al Qaeda fighting force holed up in the Arma mountain range at Shahikot. Pentagon officials said that as many as 500 enemy guerrillas were killed in six days of fighting — a number greater than their original estimate of the size of the entire al Qaeda contingent in Shahikot. Yet hundreds more continue to resist fiercely with modern weaponry and ancient tactics.

A Pentagon official said five of the seven Apache attack helicopters initially committed to the battle last weekend were disabled by machine-gun fire or rocket-propelled grenades. The helicopters were able to fly about 100 miles back to the U.S. base at Bagram, north of Kabul, the official said, but will not be considered flyable until they receive extensive repairs and are recertified as airworthy.

Army Maj. Gen. Franklin L. "Buster" Hagenbeck, the U.S. commander in the battle, requested an additional 16 Apaches. The Pentagon immediately approved the request, and the aircraft were in Afghanistan just 37 hours after the request was received, the official said, adding: "What Buster wants, Buster gets."

A U.S. military spokesman said today that 100 al Qaeda fighters and their allies were killed during intense fighting on Wednesday.

The spokesman, Army Maj. Brian Hilferty, told reporters at the Bagram air base that he had no reports of new American or Afghan casualties. So far, eight U.S. soldiers have been reported killed in six days of combat at Shahikot, more than the total killed previously during the war in Afghanistan. More than three dozen others have been wounded. At least seven Afghan fighters have been killed.

Although Pentagon spokesmen continued to assert momentum in the battle of Shahikot, the arrival of fresh troops appeared to indicate that military strategists believe they need a more robust detachment to finish the job without permitting al Qaeda fighters to slip away into the snow-covered mountains, as they did at Tora Bora in December.

The current force, consisting of about 1,000 U.S.-trained Afghans, more than 1,000 U.S. soldiers and 200 troops from such allied countries as France, Australia and Norway, has established what has been called a "security belt" around the al Qaeda positions. However, the massive peaks and inhospitable terrain around Shahikot may be impossible to encircle completely without more manpower.

"The region is difficult to secure," said Said Mohammed Isshaq, the security chief for Gardez. "This is the last pocket of al Qaeda. They will not leave it easily. They will resist."

Just as at Tora Bora, the enemy fighters have taken refuge in a mysterious and unmapped cave network, making them hard to find and even harder to pursue. "There are lots of caves — more than Tora Bora, bigger than Tora Bora, more dangerous than Tora Bora," Isshaq said.

A Pentagon official cast doubt on the notion that this battle would be the last of the war. American planners, he said, assume that there are at least two more pockets of diehard al Qaeda fighters and that they will have to be attacked in a similarly grueling fashion.

Some of Afghanistan's most powerful militia commanders decided at a meeting in Kabul this week to assist the effort to clear out the caves by sending their own troops to join the coalition based in Gardez. Gen. Mohammed Fahim, the defense minister in the interim Afghan government, asked Abdurrashid Dostum of Mazar-e Sharif, Karim Khalili of Bamian and Khan Mohammed of Kandahar to contribute forces, according to Isshaq, who was at the meeting.

Commanders intend "to start a ground offensive in three days," Isshaq said. Other Afghan sources have said a concerted ground attack was being prepared for Sunday or Monday.

At the Pentagon today, Defense Secretary Donald H. Rumsfeld seemed to suggest similar timing when he said the offensive could wind up this weekend or next week. But he added that it was difficult to know how many of the deeply entrenched and well-supplied guerrillas were still involved in the fight.

"It strikes me that it should end — I would think it would end — sometime this weekend or next week. But one can't be sure," the secretary said in response to a question from a Pentagon employee during a town hall-style meeting.

While details about the fighting remained scarce, one senior defense official with access to battlefield reports described two instances this week in which U.S. warplanes killed relatively large concentrations of al Qaeda fighters.

One occurred outside a complex of mountain caves. "About 100 to 200 al Qaeda ran out of the caves, probably thinking we were going to bomb them inside," the official said. "We rolled in on them with A-10s" — attack planes designed for striking tank columns.

In another attack, the official said, U.S. forces spotted a convoy of about 50 al Qaeda fighters moving toward the center of the battle zone, possibly attempting to reinforce other guerrillas. They also were hit by U.S. warplanes.

For U.S. military commanders, who have spent most of the five-month war in Afghanistan plotting bombing targets while Afghan guerrillas have done the ground fighting, preparing for a final ground assault represents a shift in strategy. The United States has committed its troops to a major battle here for the first time, and the initial attempt to launch a direct thrust at Shahikot ended in embarrassment last weekend.

A contingent of 600 Afghan soldiers hired and trained by the United States was forced to retreat last Saturday morning in the opening stage of the battle when it came under mortar fire from al Qaeda fighters in Shahikot before it had fired a shot. Since then, U.S. military commanders have opted for heavy bombardment and tightening the security belt rather than a head-on push.

The botched opening drive has provoked considerable second-guessing among Afghan leaders, who considered it evidence that U.S. soldiers do not understand how to fight a ground war in Afghanistan.

"The main mistake was we didn't have enough information about the enemy. We didn't know how many al Qaeda were there, we didn't know about the trenches, about the caves, about any of it," said Said Qasem, an Afghan soldier who has been working with the Americans.

Several soldiers and commanders said the Americans should not have put the Afghan fighters in big trucks that presented easy targets and should have secured the gorge leading to Shahikot before proceeding. "I would have let my people get out of the trucks and cars, get on their guard, split into [small] groups and secure some high positions for security," said Khel, a commander. "But the Americans put all of the men in one truck and just went forward."

Several U.S. soldiers interviewed by reporters at Bagram air base recalled a harrowing experience that day as well. Sgt. Robert Healy, who arrived at the battle aboard a Chinook helicopter, told the Reuters news agency: "Two minutes after we got out, we started taking hits. There were [rocket-propelled grenade] hits all over the place."

Three of his company's four medics were hurt in the fighting, which dragged on through much of the day until attack helicopters helped the U.S.-led forces withdraw. "They had their act together," James Rissler, 24, a medic hit by shrapnel, said of the enemy forces. "We were hitting them too, but not in the kind of numbers we wanted."

Commanders are eager to avoid the same scenario in any future ground assault. So, today, bombers continued to try to soften up the al Qaeda and Taliban holdouts. Largely unseen during daylight hours on Wednesday, the B-52, F-16 and other warplanes returned in force this morning. Afternoon clouds and dust storms eventually gave way to another nighttime fireworks barrage that could be seen and felt here in Gardez, about 20 miles from Shahikot, as the roar of jet engines kept residents awake and on edge.

Even Afghan officials critical of past U.S. mistakes expressed confidence that the augmented units would eventually destroy the remaining al Qaeda and Taliban forces.

"Now they have proved that they will clean up everything," Isshaq said. "They will not let any of them get away."

Staff writers Bradley Graham and Thomas E. Ricks in Washington contributed to this report.