A battalion of paratroops from the 173rd Airborne Brigade set up a new camp here tonight, moving 40 miles under heavy security precautions from the Bashur airfield where they parachuted in a week ago to set up a regular U.S. military presence in the Kurdish autonomous zone of northern Iraq.

Col. William Mayville, commander of the brigade, portrayed the move as a way to increase pressure on the Iraqi troops defending government-held territory to the south. Irbil is a dozen miles from the line separating Iraqi government territory from the 17,000-square-mile Kurdish-run zone.

"We are going up there with the express purpose of backing up the ultimatum, which is capitulate and join a free Iraq, or failing that, you will be buried where you are killed," he said in an interview.

Task Force Red Devil, under the command of Lt. Col. Harry Tunnell, moved the 40 miles from the airfield on winding roads over mountains, driving in blackout conditions for the last stretch to preserve security. The initial forces were carrying heavy loads of ammunition, scrimping on food, water and other supplies to make room.

In towns along the way, Kurdish residents stood by the road watching the long convoy roll through, cheering and raising their arms in triumph. Kurdistan Democratic Party militiamen waved the convoy through checkpoints.

A battalion-sized Iraqi force is dug into a ridgeline less than 15 miles from the new American position, which lies in territory controlled by Kurdish militias since the 1991 Persian Gulf War. Portions of 10 Iraqi divisions, including armor, mechanized and artillery units, are also in the region. Iraqi artillery is believed to be out of range of the U.S. force, but the closest Iraqi positions were hit by airstrikes last night.

Of greater concern, Mayville said, are Iraqi missiles, including Ababil-100s, which have the range to reach the U.S. force. Brigade officers say it is possible but unlikely that Iraqi forces in the north would use chemical weapons against U.S. troops.

The primary mission of U.S. forces in northern Iraq is to discourage Turkish troops from crossing the border in force. A flow of displaced Kurds north toward the Turkish border could trigger such an incursion.

A battalion of paratroops from the 173rd remains at the Bashur airfield, guarding the rapidly growing American lodgment. Detachments of troops and equipment from various Army and Air Force units continue to arrive at the airfield and reinforce the brigade.