Shimmering in the mountain light, the airstrip dominates a majestic valley just below this neatly ordered Kurdish town deep in northern Iraq. The 1.5-mile runway, built in the 1980s by the Iraqi military, has lain derelict for a dozen years. But in the hands of the Kurdish militias that govern northern Iraq, its edges show signs of recent grooming.

Bright white tents flank either end of the macadam. At the freshly installed sentry post, new red paint shines on a wooden drop-barrier. Standing behind it, a Kurdish militia officer politely waves away a visitor, saying "there is no one here."

The recent renovation of two such airstrips in the Kurdish-run zone is the most public evidence of a discreet but active U.S. military presence here. In months of work inside Iraq's Kurdish region, according to officials here and in Washington, U.S. teams have prepared the way for an American-led invasion force expected to number in the tens of thousands. If Turkey's parliament votes to allow the 4th Infantry Division and other U.S. forces to enter Iraq from Turkey, the teams will help ensure they find an easy foothold in the country's mountainous north.

Residents say the runway at Harir, about 30 miles northwest of Irbil, does not seem to be in use yet. The only air traffic heard in town, they say, is the distant roar of high-altitude U.S. or British warplanes enforcing the northern "no-fly" zone, and the occasional buzz of a helicopter.

An officer with the Kurdistan Democratic Party, which administers the region around Harir, said the helicopters belonged to Turkey. The neighboring state has stationed several thousand troops inside northern Iraq for years, to hunt Kurdish separatists who fought a guerrilla war inside Turkey until 1999. At another disused Iraqi military airfield at Barmani, about 15 miles south of the Turkish border and 30 miles east of Zakhu, the runway is lined by Turkish tanks.

Another lengthy and long-neglected airstrip has been undergoing renovations in Bakrajo, a town on the outskirts of Sulaymaniyah, 100 miles southeast of here. In mid-January, municipal firetrucks sprayed off the mud and stones that had collected on the asphalt strip since Iraqi forces abandoned it after the 1991 Persian Gulf War. At the same time, Kurdish militiamen dug bunkers and fighting positions along the roughly two-mile length of the runway.

A steady stream of dump trucks carted in gravel last week to restore a muddy access road running from the main highway. A lone sentry at the main road appeared to be an ordinary member of the pesh merga, or "those who seek death," as the Kurdish militiamen are known. But a pair of guards who crossed a mucky field to intercept approaching reporters identified themselves as Kurdish special forces, a corps that normally guards senior officials of the Patriotic Union of Kurdistan, which administers the zone around Sulaymaniyah.

Rick Francona, a retired Air Force lieutenant colonel who once served as military intelligence liaison to the Iraqi military, said the Bakrajo and Harir airstrips would be "excellent places to set up pre-positioned gas stocks for your helicopter operations." The road beside the Bakrajo field leads to Kirkuk, 75 miles to the west, and to the oil fields that invading U.S. forces would attempt to secure in the first phases of any attack, according to U.S. officials and analysts.

That would suit Bahroz Karim Abdul, a farmhand who has watched the renovations at Bakrajo unfold for weeks from the flat concrete roof of the barn he tends beside the airfield. Iraqi forces killed one of his daughters during a Kurdish uprising in 1991 that was suppressed by Iraqi helicopter gunships. Before the airfield was taken by pesh merga, he said, some Iraqi helicopters flew from Bakrajo.

Built as secondary military airfields to use for emergency landings and in case other fields came under attack, Bakrajo and Harir are long enough to accommodate most aircraft. But Francona was unsure their decks were thick enough to withstand repeated landings by fully laden U.S. C-5 and C-17 military transports.

The absence of control towers is not a major problem; military flights can be guided "from a jeep," said Thomas G. McInerney, a retired Air Force lieutenant general. But the fields are bracketed by nothing but mountains and sheep: No fuel depots, aprons or other aviation infrastructure are visible.

As a result, they would not be a substitute for full-fledged Turkish air bases, analysts said. Airborne and special operations forces could get along with such spartan conditions, the former officers noted, but large masses of infantry would not come into northern Iraq easily by air.

"You have to bring in big airplanes that are vulnerable to Iraqi fighter aircraft," McInerney said. "We would have a fighter cap flying that would take care of them, but it's a big job." And preparations to receive planeload after planeload of infantry "would take weeks," he added.

Kurdish farmhand Bahroz Karim Abdul shows his battle scars in front of the Bakrajo airfield, which is being renovated.