U.S. warplanes have significantly reduced their bombings of northern Iraq this year, with pilots concerned that Saddam Hussein is hiding his guns in civilian areas and could shoot down an American plane.

Recently, Iraqi gunners have opened fire almost every day, according to American pilots, and experts say Saddam has beefed up his missile forces with Chinese and possibly Yugoslav help.

Nearly six months into this year, U.S. warplanes patrolling a no-fly zone over northern Iraq struck at targets just seven times, despite Iraq's having opened fire on the aircraft 48 times. The United States struck 47 times in all of last year.

The dangers and the estimated $1 billion cost have led officials in Washington to question a mission that has sent more than 200,000 flights over Iraq during the past decade.

"With every day that goes by, the odds ... of losing an aircraft go up," said Col. Maury Forsyth, the U.S. officer who draws up the allied flight plans for the northern no-fly zone. He spoke from his concrete command bunker in Incirlik air base in southern Turkey.

Saddam "is doing everything he can to shoot us down," Forsyth added.

Forsyth said the Iraqis have continuously been shooting during his 22 months in command of the aircraft. Saddam recently has been hiding some of the anti-aircraft guns in civilian areas.

"I prefer to ... stay away rather than endanger the civilian population," Forsyth said. "That may account for some of the decrease" in U.S. strikes.

Pilots say the shooting is constant.

"It seems like you see a gunner almost everywhere in the no-fly zone," said Navy Cmdr. Tom Tack of Allen Park, Mich.

Iraq has apparently ordered its gunners to shoot as much as possible to down an American aircraft, according to experts.

"It would be an enormous propaganda victory," said Nick Cook of Jane's Defense Weekly.

Experts say Iraq apparently hired Chinese workers to use fiber-optic cables to link up its radar systems -- an allegation noted by Defense Secretary Donald H. Rumsfeld on a visit to Incirlik this month, but denied by the Chinese government.

"We've been very fortunate that we've not had a loss," Rumsfeld said at the time. "The risk grows to the extent that other nations assist Iraq in strengthening its military capabilities, its air defense capabilities."

The radar network would give Iraqi commanders an overall picture of the allied flights and help them direct anti-aircraft fire. The surveillance radar that watches planes is located outside the no-fly zone.

Other reports say Slobodan Milosevic, while president of Yugoslavia, dispatched air defense experts to advise the Iraqis on how to improve their anti-aircraft capabilities.

During the NATO bombing of Yugoslavia in 1999, anti-aircraft missiles and artillery scored a number of hits on U.S. and allied planes, bringing down an F-117 stealth bomber and an F-16 Fighting Falcon, and damaging others. The Yugoslav defenses forced NATO to order its pilots to remain at altitudes of over 16,400 feet, from which it proved difficult to strike entrenched troops in Kosovo.

Some of the squads in NATO's Yugoslav campaign now operate over northern Iraq.

The no-fly zone was set up in 1991 after the Gulf War to protect rebellious Iraqi Kurds from Saddam's forces. A similar zone was set up over southern Iraq a year later and is also patrolled by U.S. and British aircraft.

The job of patrolling the zones became more dangerous in December 1998, when Iraqi gunners began routinely firing on the aircraft.

On Monday, some 40 aircraft streaked down the runway at Incirlik air base toward northern Iraq. U.S. F-15 fighters armed with air-to-air-missiles flew first and were quickly backed up by F-16 fighters carrying anti-radar missiles.

Radar jamming aircraft and planes carrying laser-guided bombs also joined the mission. The bombers are there to attack any site that opens fire on the other planes.

Pilots said that although Iraqi gunners fire often, their chances of hitting an aircraft are slim.

"I think the threat is fairly minimal, but there is always the threat of a lucky shot," said Tack, who flies an EA6-B Prowler, an aircraft designed to jam enemy radar.

The Iraqis are so afraid of U.S. anti-radar missiles that they usually fire their missiles without turning on their short-range targeting radar, giving them little chance of hitting an aircraft, pilots say. Unlike the surveillance radar, the targeting radar is located within the no-fly zone and is therefore vulnerable to U.S. attack.

Although the volume of Iraqi firings appear to have increased, pilots say Iraqi gunners with heavy machine guns usually fire only short bursts.

"It's almost like the gunner fires and runs away," said Tack. "We never see more than a single or two air burst explosion."

The success of the mission is clear.

More than 200,000 flights have been flown without a single plane damaged. No Iraqi plane has violated the northern zone since November, 1999, a violation that ended without incident.

"From the military perspective, it has worked," Tack said. "We've kept him in his little military box that we let him play in."

But with the dangers growing, Washington is reconsidering the mission.

According to some experts, that could include phasing out the daily patrols, but ordering aircraft to respond immediately if Iraqi forces threaten the northern Kurdish enclave.