The Bush administration is conducting an overall review of Iraq policy, which officials hope will be completed by the summer.
A Pentagon official told the Washington Post newspaper that the commanders were worried by the increasing threat of a plane being shot down by Baghdad's air defences.
The Bush administration is conducting an overall review of Iraq policy, which officials hope will be completed by the summer.
The two no-fly zones were created by the US, Britain and France soon after the Gulf War. One zone is to the north of the 36th parallel, with a second to the south of the 33rd parallel.
The US and Britain have been carrying out attacks on Iraqi targets since late 1998.
They say the attacks were carried out whenever Iraqi air defences locked onto aircraft patrolling the no-fly zones.
Baghdad says more than 300 civilians have been killed in the attacks, but the two Western powers dispute some of these figures and say they do not target civilian areas.
US commitment
Administration officials said on Tuesday that the US remained committed to maintaining the zones.
But Army General Tommy R Franks, who heads the US Central Command and enforces the southern no-fly zone, recommended reducing the number of patrols but maintaining a minimum number to check possible movements of Iraqi troops towards the Saudi and Kuwaiti borders.
And Air Force General Joseph W Ralston, in charge of the northern zone, said he would prefer to halt flights altogether.
Aircraft could be kept at the ready in case Iraq flew warplanes in the zones to harass Kurds in the north or Shi'a Muslims in the south, he added.
Another top commander was quoted as saying that the risk of losing a pilot was becoming so great that it might be necessary to stop the operation.
He added that Iraqi anti-aircraft guns were firing on almost every flight and had launched well over 100 surface-to-air missiles since the last large-scale US and British raids in February.
The northern zone was established after Baghdad mobilised helicopter gunships to quell a Kurdish uprising. The southern zone was imposed to protect Shi'as who also rebelled against Baghdad.
