About 1,000 paratroops from the Army's 173rd Airborne Brigade parachuted onto a strategic airfield in Kurdish-controlled northern Iraq tonight to open a northern front in the war against Iraq. The operation is also aimed at discouraging Turkish troops on the border from crossing into Iraq in large numbers, a move that could precipitate fighting with Kurdish forces.

With cries of "Go! Go! Go!" rising above the roar of jet engines, jump masters aboard one of the many Air Force C-17s carrying the U.S. force gave the signal to leap. Inside the darkened plane, four long rows of paratroops braced to leap out. Lt. Col. Harry Tunnell, a lanky battalion commander, led a column of paratroops out one of the jump doors, and a second column rushed out the door on the plane's opposite side.

One by one, nearly a hundred paratroops in desert camouflage uniforms disappeared from the plane, each bearing heavy loads of weapons and equipment to sustain them on the muddy ground below. Dust blew in the doors as the paratroops poured out.

In a minute, it was over, and the C-17 climbed steeply, an evasive maneuver in case of enemy fire. Initial reports from the field indicated that the landing went well, said officers at Aviano air base in northern Italy, where the troops assembled before the mission.

"Americans are asking you to make the world a better place by jumping into the unknown for the benefit of others," Col. William Mayville, the brigade commander, told the paratroops before they boarded.

"Paratroopers, our cause is just, and victory is certain," he added. "I want you to join me tonight on an airborne assault."

The force dropped into the airfield near Harir, about 45 miles northeast of the north Iraqi city of Irbil, includes rifle companies, platoons armed with mortars and antitank missiles, engineers for clearing mines, sniper teams, long-range surveillance teams, Air Force ground teams and Humvees equipped with grenade launchers and .50-caliber machine guns. Heavy weaponry, equipment and more troops to support and expand the brigade's position will arrive in coming days, officers said.

The complex undertaking takes the airborne brigade into an area controlled by the Kurdistan Democratic Party, one of two Kurdish groups governing an autonomous area that had been protected by U.S. and British fighter patrols.

It places the U.S. forces at a location where commanders say they can influence the actions of all Iraqi, Turkish and Kurdish forces, including the Patriotic Union of Kurdistan, the group governing the other part of the zone. The brigade, based at Vicenza, Italy, is also positioned for involvement in the key cities of Irbil and Kirkuk, commanders said.

Backed by heavy air cover, and working with U.S. Special Forces troops already on the ground, the airborne brigade is also prepared to fight Iraqi forces it encounters and could be launched to seize key strategic objectives both inside and outside Kurdish-controlled territory, officers said.

But one of the brigade's immediate aims is to keep the estimated 40,000 Turkish troops on the border from starting a "war within a war" with U.S.-backed Iraqi Kurd forces.

Turkey fears that the Kurds' involvement in the war in Iraq would give them leverage to cement a united autonomous zone. That, Turkey believes, could awaken similar demands among its Kurd minority.

After several days of mixed signals from Turkey's political leaders, the chief of the Turkish armed forces said today that Turkey would coordinate any additional deployment of troops to northern Iraq with the United States, backing down from previous threats to send forces across the border over U.S. and Kurdish objections.

The military wields tremendous influence in Turkey, and the statement by Gen. Hilmi Ozkok was seen as the most reliable sign that Turkey was backing down, simplifying the Pentagon's plans for a northern front.

Establishing a northern front has been a high priority for the U.S. Central Command, as is plainly evident by the fleet of C-17 transport aircraft assembled to move the brigade. The number of planes being used is classified, but it represents a significant portion of U.S. airlift capacity worldwide. War planners have also assigned an array of surveillance aircraft and a large number of fighter combat sorties to provide close air support to the brigade.

"If you look at the assets being thrown into this mission, it's absolutely incredible," a senior officer said.

Nonetheless, the overall size of the operation is significantly smaller than initially conceived by U.S. war planners. The earlier plan would have had the Army's 4th Infantry Division invading Iraq through Turkey. The 173rd Airborne was to accompany the armored force on the attack. Instead, because Turkey refused to host U.S. troops, the light infantry brigade represents the United States' major ground combat force in the north.

Near the border with the Kurdish-controlled region are 10 Iraqi army divisions, including one from the elite Republican Guard, near Mosul.

Airstrikes directed by U.S. Special Forces in recent days have damaged several of the Iraqi divisions, none of which is near full strength, according to intelligence officers. They expect some of the units will capitulate with the arrival of a large U.S. force.

However, some of the Iraqi units have shown aggressive behavior and are expected to fight, in particular the 16th Infantry Division.

[On Thursday, a series of airstrikes hit Iraqi front-line positions at Kalek, sending up a large mushroom cloud. The attacks were the most intense in northern Iraq since the war began last week.]

Some U.S. officers see their biggest threat in the north as terrorism, in particular from the group Ansar al-Islam. Intelligence officers said they expect the brigade could be the target of car bombings, sniper fire or drive-by shootings.

"The Iraqis are the least of our worries," said one officer.

The brigade is well-prepared to counter the terrorism threat, Mayville said, but he added the danger is very real. "Are we going to be a target for every al Qaeda type that wants to make a statement?" he asked.

Tonight's jump caps months of frantic preparations by the 173rd.

After Turkey refused to grant U.S. forces permission to launch an attack from its territory, the brigade scrambled to change its plans.

Brigade officers described the operation as the largest U.S. paratrooper jump since the invasion of Panama in 1989. It was the 173rd Airborne's first combat jump since Operation Junction City in 1967, the only large combat tactical airborne operation in the Vietnam War.

Brigade officers had been nervously monitoring weather in the drop zone in recent days and considered scrubbing the jump because of a strong front, dubbed "the storm of the century" by military weather forecasters.

Two days of rain, thunderstorms and high winds led some officers to recommend delaying the operation. But with an elaborately choreographed schedule of refueling tankers set up and laboriously negotiated diplomatic clearances at risk, Mayville banked on a forecast that showed a window of clearing weather and made the decision this morning to launch.

Commanders had the option to fly the brigade into the airfield, which is in territory controlled by friendly Kurdistan Democratic Party forces and has been occupied in recent days by a small number of U.S. Special Forces. But they were concerned that flying a force onto a relatively primitive landing strip would take too long to build significant combat power.

Commanders also favored the psychological impact they expect the airborne assault will have on all parties in the region -- Iraqi, Kurdish and Turkish.

CorrespondentsPhilip P. Pan in Ankara, Turkey,and Daniel Williams in Irbil contributed to this report.

Iraqi positions in the north of the country are bombed, just outside the Kurd-controlled zone, where U.S. troops could face resistance.