By Nick Assinder BBC News Online political correspondent

Tony Blair will on Tuesday face a hostile Labour conference in defiant and unbending mood.

The day after he was defeated over his plans on financing the public services, and was widely attacked over Iraq, he will tell delegates he is not for turning.

His speech - widely billed as the most difficult of his leadership - will seek to win over the conference to both the private finance initiative and to his ultimate goal of dealing with Saddam Hussein.

Conference is deeply sceptical

But he will also make it abundantly clear that he is not about to change tack on either issue.

He is expected to get a rough ride from large sections of the conference, deeply concerned over the two issues which have dominated proceedings.

Cold shoulder

Some are predicting he may even get a worse reception than the icy, cold shoulder handed out to him at the TUC conference in this town just two weeks ago.

He is expected to tell delegates it is time to press harder for radical reform of the public services.

It is time to "increase the pace, not mark time or slow down", he is expected to say.

Mr Blair's aides say he will also reinforce undertakings given by Chancellor Gordon Brown that Monday's conference defeats on PFI will be ignored by the government.

And that they will not be allowed to disrupt private sector involvement in the construction of new hospitals and schools.

Serious trouble

While his Thatcheresque "I'm not for turning" message may win over a few doubters it is likely the majority of his critics will remain unconvinced.

And that could land him in serious trouble - first with the unions over PFI, and second with many in the Labour movement and the wider public over the best way of dealing with Saddam.

There is the real prospect of escalating action among public sector workers who fear PFI works against their interests and in favour of private enterprise.

The prime minister is already braced for strikes by firefighters and on the railways. And there is even talk of a long winter of disputes.

Saddam must be dealt with

But on the public services, the prime minister is caught. He has to deliver real improvements by the next election or suffer the consequences in the ballot box.

He is convinced that PFI is the best way of doing that and has to balance the risk of disappointing voters with that of taking on the unions - previously fingered as "wreckers" and "the forces of conservatism".

MPs revolt

Similarly on Iraq, he knows he has a major uphill battle ahead to sway public and world opinion.

The publication of the dossier of evidence against Saddam has done little to change minds and last week he suffered a 50 plus revolt from his own MPs on the issue.

There are also serious worries about his closeness to the Republican President George Bush.

But the prime minister wants to suggest that, unless he is alongside the president, continually urging the case for caution and the primacy of the UN, Washington may act more precipitately.

Many, however, are ready to dismiss that argument, believing instead that when push comes to shove Mr Blair will do the president's bidding.

And, while PFI and Iraq will inevitably dominate, observers will also be watching for signals of the prime ministers in tensions on a range of other issues - notably the euro and fox hunting.

What is absolutely clear is that, however the arguments run, this is an absolutely crucial speech for Mr Blair.

Decisions taken in Blackpool may count for nothing in Downing Street, but Mr Blair's standing can be seriously affected by his performance at conference.