US military officials believe they have made headway in persuading the Bush administration not to mount a military campaign in Iraq, reports say.

There are fears US soldiers could be exposed to chemical weapons

The Washington Post quotes senior Pentagon officials as saying that the Joint Chiefs of Staff mounted an "aggressive campaign" for the White House to reconsider such an attack.

This included a private briefing for President George W Bush by General Tommy Franks, the head of US Central Command.

General Franks is said to have warned that any invasion would require at least 200,000 troops - more than some officials originally estimated.

Officials told the Washington Post that the chiefs of staff were concerned about the possibility of brutal hand-to-hand fighting with Iraqi soldiers which would result in high casualties.

Refocused attitude

The generals also expressed fears that if Iraqi President Saddam Hussein felt cornered, he would unleash his arsenal of chemical and biological weapons, the officials said.

It is feared there is no viable successor to Saddam Hussein in Iraq

The Bush administration has in recent weeks refocused its attitude towards Iraq on the possibility of overthrowing Saddam Hussein through covert means, and also using international diplomacy and Iraqi opposition groups based abroad, the officials said.

Mr Bush said during his trip to Germany that he had no plans for an Iraqi invasion at present. He felt it necessary that his administration used "all means at our disposal" to overthrow Saddam Hussein, hinting that the military option was not the only one being considered.

The latest reports present a marked contrast to previous messages from the White House, which had indicated that an attack on Iraq was all but inevitable.

'Iraq hysteria'

Mr Bush's inclusion of Iraq in his "axis of evil" during his State of the Union address in January led many to believe an attack would be imminent.

But in April the Bush administration denied a report - this time by the New York Times - that said the military strategy for an attack had been worked out.

The officials told the Washington Post that one general had expressed relief that much of the "Iraq hysteria" had been at least partially defused.

Some of the chiefs have reportedly felt that the ageing Saddam Hussein had improved his behaviour in recent months. They were also concerned that he appeared to have no successor the administration felt it could deal with.

However, the paper reported that it may be difficult to persuade other, more hawkish, Republican officials to soften their line towards Iraq, with one military official quoted as saying that the chiefs' plans "smack(ed) to me of risk aversion".