The 193 UN countries closed in Thursday on the first-ever global treaty to regulate the $80 billion a year conventional arms trade.
While diplomats were cautiously optimistic that the landmark accord would be agreed at the final negotiating session starting at 1900 GMT, doubts remained over whether India, Iran or Syria could block the required consensus.
Rights groups say the proposed accord is too weak. But Britain's UN ambassador Mark Lyall Grant said it is "time for all countries to rally round (the) strong president's text."
Talks have been held on the treaty since 2006 after years of pressure for measures to restrain a trade that rights groups say is fueling conflict, terrorism and crime around the globe.
The UN estimates that 500,000 people a year are killed in armed violence.
The treaty would cover tanks, armored combat vehicles, large-caliber artillery systems, combat aircraft, attack helicopters, warships, missiles and missile launchers and small arms and light arms.
It would aim to force countries to assess whether the sale of a weapon could be used for genocide, war crimes or by terrorists or organized crime gangs.
Negotiating conference president Peter Woolcott of Australia handed out what he called a "take it or leave it" text to UN states on Wednesday and gave them 24 hours to consider their response.
Diplomats said they did not expect the major arms producers -- the United States, Russia, Germany, France, China and Britain -- to block the treaty.
Some said, however, that Russia could refuse to sign the accord, which could weaken its application.
"Moscow believes the text is not strong enough on arms trafficking and that it should explicitly mention 'non-state actors'", such as the Syrian and Chechen rebels, said one European negotiator.
China and Russia also had concerns about the reporting of arms sales.
The latest text says that "reports may exclude commercially sensitive or national security information."
Diplomats said India could still block the accord because it does not want the controls to cover arms transferred under bilateral military agreements.
The United States opposes ammunition coming under the full controls imposed by the treaty. Ammunition has, however, been left in an annex which does not impose compulsory monitoring of trade in bullets, for which the United States is the biggest producer.
Changes made since the start of the talks on March 11 have made "significant improvements," said Britain's chief negotiator Joanne Adamson.
Adamson highlighted "a new article on preventing diversion of arms and (a) strengthened section on exports which are prohibited."
The British negotiator said "human rights are at the heart of this text. With this text, we should be able to meet our objective of a strong treaty with broad support."
"It is not everything that we wanted, but it will be the first treaty on an industry that causes much suffering and there are benchmarks," said a European ambassador, speaking on condition of anonymity.
Amnesty International is "disappointed" that "the scope of the treaty remains short of what types of arms should be covered," despite concerns expressed by many governments, said the group's arms control specialist Brian Wood.
But he predicted the treaty would be adopted on Thursday.