NORTHERN IRAQ - After two weeks deep in Kurdish-held territory, elements of the 173d Airborne Brigade, now supported by newly arrived tanks from the First Infantry Division, moved south yesterday to within 20 miles of the oil-rich city of Kirkuk.

Turkish Prime Minister Recep Tayyip Erdogan had said earlier that Kurdish control of Kirkuk or nearby Mosul would be grounds for a Turkish invasion of northern Iraq. Turkey and its neighbors Syria and Iran fear that Kurdish control of the region and its oil would create a source of income to purchase weapons for use in trying to create an independent state called Kurdistan, spanning an area that today covers parts of the four countries.

Turkey has an estimated 40,000 troops along its 218-mile border with Iraq.

There are only an estimated 3,000 U.S. troops in northern Iraq, and it is unclear how they would prevent Kurdish fighters from taking the cities or the local Kurdish population from rising up against the remnants of Saddam Hussein's forces and taking control.

"Entering northern Iraq will not be on the agenda as long as Iraq's territorial integrity is preserved and there is no move aimed at seizing the oil of Mosul and Kirkuk," Erdogan said Monday.

The first forward elements of the U.S. force had moved out of Bashur Air Base late Tuesday, just hours after the first M1 Abrams tank rolled off a C-17 transport plane. The rest of the brigade, with an unspecified number of tanks and Bradley Fighting Vehicles, is to follow.

Commanders say they cannot discuss their plans publicly, but they promise that a ground attack against Iraqi forces arrayed along the line with the Kurdish region is not far off. A convoy of Kurdish guerrillas driving jeeps mounted with multiple rocket launchers and towing artillery pieces was seen late yesterday near Chamchamal, 20 miles east of Kirkuk. The commander said the guerrillas, known as peshmerga, had been ordered to deploy on the front lines close to Kirkuk.

Iraqi forces at Mosul and Kirkuk, estimated as high as 40,000 troops with hundreds of tanks, have been pounded for weeks by air strikes directed by 10th Special Forces Group soldiers operating in the area.

Tuesday night, as the 173d paratroopers bedded down in a grassy field, thunderous booms erupted in the distance. Air Force combat controllers traveling with the paratroopers said U.S. B-52 bombers were dropping loads of 2,000-pound satellite-guided munitions on the Kirkuk positions.

The special forces have been aiding Kurdish fighters in small ground battles against Iraqi forces. On Monday night, as many as 150 Iraqi soldiers were killed in one such encounter, special forces officers said in a briefing Tuesday. Two Iraqi prisoners were taken and were being interrogated by Kurds in the basement of the compound. Soldiers of the 173d said they observed Kurds beating one bound prisoner.

The special forces briefing offered insight into what essentially has been a low-visibility, nonconventional northern front: Small numbers of highly trained U.S. troops, backed by air strikes, have helped Kurdish peshmerga forces push Iraqis miles from their original positions.

"They have just fallen back completely," said Sgt. Tom Flaherty, standing in front of a map studded with decals representing the locations of special forces teams and Iraqi units. But, he said, "they're dug in pretty good."

The central issue is whether the Iraqi troops in the north, including those arrayed around Kirkuk, will fight to the death or surrender.

Brigade officers of the 173d acknowledge that their force is not large enough or strong enough to attack and defeat several mechanized divisions. What the highly mobile paratroopers can do, though, is secure key locations and destroy parts of the Iraqi lines in hit-and-run operations as they wait for the regime to collapse.