It began as a routine supply mission to the front lines, in a volatile but largely becalmed city.

It ended as a fiery and chaotic rescue mission, with a small force of Marine tanks, Humvees and ground troops surrounded and attacked as they fought their way through a hostile neighborhood to save the crew of a burning armored personnel carrier.

Marine officials said the three-hour battle that erupted at dusk Tuesday on the streets of Fallujah, and was recounted Wednesday by several of the key officers involved, exemplified the bravery and resourcefulness that Marines are known for, even when surprised and surrounded by a host of enemy fighters on alien urban turf. By the end of the tumultuous encounter, the charred personnel carrier had been towed to safety by a tank and most of its 17 crew members -- several of them wounded -- had been rescued from a house where they had taken shelter.

But the incident also revealed some startling facts about the insurgency that the Marines are facing here, officers said. More dramatically than any armed confrontation since U.S. forces surrounded Fallujah nine days ago, it showed the tenacity, coordination, firepower and surprisingly large numbers of anti-American guerrillas who still dominate much of the city.

"We definitely stumbled into a wasps' nest. They were definitely a lot more organized than we thought," said Capt. Jason Smith, 30, commander of the company whose armored supply vehicle made a wrong turn into insurgent territory and was immediately inundated by gunfire and rocket-propelled grenades from all sides.

Marine officials here said offensive operations in Fallujah would remain suspended, extending a pause that was ordered Friday to allow civilians to leave the city and let political leaders in Fallujah and Baghdad attempt to negotiate a solution to the conflict.

Just before dawn Wednesday, however, AC-130 Spectre gunships launched a devastating punitive raid over a six-block area around the spot where the convoy was attacked, firing dozens of artillery shells that shook the city and lit up the sky. Marine officials said the area was virtually destroyed and that no further insurgent activity had been seen there.

According to accounts by Smith and two other officers, a supply convoy of Humvees was heading toward a command post at the edge of a Marine-controlled industrial zone around 4:30 p.m. Tuesday when it came under small-arms fire. The convoy backtracked, and its cargo was shifted to two Marine amphibious assault vehicles, which resumed the mission.

Those carriers were hit by rocket-propelled grenades, known as RPGs. One turned back toward friendly territory, but the other caught fire and the driver lost his way in the unfamiliar neighborhood. Suddenly, the crew encountered a large number of armed men milling in the streets. Within minutes, they were being attacked from all sides.

"They started taking RPG fire and tried to get out of the area, but we lost communication with them," Smith said. "Their engine was on fire and they were heading away from our zone. . . . I saw a huge plume of smoke and I knew something was very wrong."

Officers dispatched a quick-reaction squad whose members had already been in battle earlier Tuesday. While guarding the site of a helicopter crash in a marshy area southeast of the city that morning, the outfit was ambushed by insurgents.

The rescue squad rushed four tanks and six Humvees to the area, where they fought their way through several blocks to reach the burning carrier. Surrounded by 25 Marine riflemen on foot, the armored vehicles advanced, firing machine guns from their turrets. Overhead, Air Force attack planes repeatedly strafed the area. Marine officials here said at least 20 insurgents were shot dead during the fighting.

"Within the first 500 meters, we were shooting 360 degrees," said Lt. Joshua Glover, 25, who commanded the rescue force. "When we finally saw the [armored personnel carrier], it was a piece of burning metal."

The carrier's crew had managed to escape and had taken shelter in the nearest house, where they were pummeled with gunfire from the surrounding houses. Under covering fire from U.S. tanks and planes, Glover's team was able to get the crew into Humvees and race off to safety.

"People were tossing grenades from the houses on either side," Glover said. "I could hear small-arms fire, and I even saw people running across the street to try and enter the house." He and Smith said they saw only armed men in the area.

Senior Marine officials here, who plan to seek commendations for valor for four men involved the rescue mission, said the most important aspect of the incident was the courage that the Marines displayed in battling their way through heavy fire to reach the disabled carrier and rescue its crew.

"This is a story about heroes. It shows the tenacity of the Marines and their fierce loyalty to each other," said Lt. Col. Brennan Byrne, commander of the 1st Battalion, 5th Marine Regiment. "They were absolutely unwilling to leave their brother Marines behind."

At the Marine base in Fallujah and at command posts along the front lines Wednesday, troops recounted the rescue story to one another, relishing every detail and braced by the display of fighting spirit during what, for many Marines, has been a period of frustration and inactivity since Friday, when offensive operations were halted.

But Smith and other officers said the incident also offered sobering insights into the sophistication and size of the insurgent force, which the Marines have characterized as a combination of Iraqis loyal to toppled president Saddam Hussein, foreign Islamic guerrillas and local criminals.

In the past several days, Marines have also recovered hundreds of weapons, including rocket launchers, machine guns, sniper rifles and explosive belts for suicide bombers, while searching the deserted industrial zone. Many of the weapons were wrapped in plastic and buried under sand piles or other debris, suggesting they had been hidden some time ago for use in battle.

Until Tuesday's firefight, moreover, the Marines here had never been attacked by more than five or six insurgents at once, Smith said. This time, when the personnel carrier strayed just a few blocks into enemy territory, "there were 50 to 100 guys. It took a great deal of fire for us to get there, and I saw much more coordination than anything I seen before," he said.

"They've been preparing for this the whole time."

Staff Sgt. Daniel Santiago readied his Marines to leave their base in southeastern Fallujah on Tuesday, when the Marines came under intense attacks in the city. A Marine amphibious assault vehicle moved toward a battle in Fallujah on Tuesday. A similar vehicle was inundated by gunfire and rocket-propelled grenades after it strayed into a hostile neighborhood that day.