UN Secretary General Kofi Annan is to tell the General Assembly they have reached a crossroads over the issues of peace and security.
Annan will tell the UN they have some tough choices to make
He is expected to criticise President Bush's doctrine of allowing the US to take pre-emptive military action when threatened.
Mr Annan will say this could lead to "a proliferation of the unilateral and lawless use of force".
He will ask if such moves should be supported by the Security Council.
Council members may need to start discussing the terms under which collective action through a council resolution might authorise a pre-emptive strike against a threat such as that posed by terrorist groups armed with weapons of mass destruction, Mr Annan will say.
This would be a major departure from the UN Charter, which until now has sought to deal with potential threats through a policy of deterrence or containment, says the BBC's Greg Barrow at the UN.
Edward Mortimer, head of the speech-writing department at the UN Secretary General's office, believes the speech is a direct challenge to the US doctrine.
"It is also a challenge to those who share the Secretary General's anxiety about that doctrine, because he says it is not enough to be against unilateralism," he told the BBC's World Today programme.
"You have to show that collective mechanisms and decisions can actually address the concerns which are driving some states to take unilateral action - because it is those concerns or feelings of vulnerability that some sates have which are driving them to take unilateral action."
In his prepared address, released in advance, Mr Annan will also tell the assembly he is to establish a panel of eminent personalities to carry out a wide-ranging examination of the UN's role in addressing challenges to peace and security.
It will look not just at the way bodies like the UN Security Council work but also how they can become more effective.
UN member states are faced with a decision no less important than the one they faced when the United Nations was founded in 1945, he will say.
After the 11 September 2001 terrorist attacks, US Defence
Secretary Donald Rumsfeld developed an argument for
taking pre-emptive action against enemies who could launch
a surprise chemical, biological or nuclear attacks.