By David Willey BBC Rome correspondent

A leading American Catholic theologian has justified a US war against Iraq as a just war according to Catholic doctrine, at a lecture in Rome sponsored by the US embassy to the Vatican.

The Pope has expressed strong opinions against a war in Iraq

Professor Michael Novak argued that the US was already engaged in what he called an "asymmetric war" against the Iraqi leader Saddam Hussein, in the sense that the first Gulf War had never come to a proper end.

He quoted the Catholic catechism as to what constitutes a just war in modern times and claimed that US President George W Bush's planned attack falls within the definitions approved by Church authorities.

"I think we should learn that appeasement and weakness bring violence and seriousness of purpose and strength bring respect," he said.

Others unconvinced

Although Mr Bush's ambassador to the Pope insisted that Professor Novak was giving his own views as a Catholic layman and a respected theologian and not those of the US government, the professor made a forceful defence of White House policy on Iraq.

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He was speaking to an invited audience of diplomats, university teachers and priests about US plans to forcibly disarm Saddam Hussein.

He argued that a pre-emptive US war against Iraq came under St Augustine's conditions for the waging of a just war.

Afterwards I asked Father Gerry O'Collins, a distinguished teacher of moral theology at the Papal University here, if he was convinced by Professor Novak's arguments.

"No I don't think so," he said.

"I think many of us were glad to hear the other side... a lot of people came here tonight not accepting, standing very firmly with the US bishops and the British bishops and the Pope against the war.

Pope's opposition

"And if that's the best, then it's not very convincing, what Novak had to say."

The Pope's envoy is due in Baghdad for talks with the Iraqi leader

Professor Novak met officials at the Vatican's Justice and Peace Council during his weekend stay in Rome.

However the newly-appointed president of that Vatican department, Archbishop Renato Martino - for 16 years the Vatican's permanent envoy at the United Nations in New York - pointedly decided not to attend.

The Pope has expressed his strong opposition to the idea of war as a solution to the present Middle East crisis, and has dispatched a senior Vatican cardinal to Baghdad for talks with Saddam Hussein.

And on Friday the Pope will receive the deputy Iraqi premier, Tariq Aziz, at the Vatican.

Mr Aziz, a Catholic, will pray for peace at the tomb of St Francis in Assisi the following day.