* UN aid chief says Libya's centralized system an issue
* Amos calls for truce to allow supplies to get through
UNITED NATIONS, May 9 (Reuters) - The way that sanctions are applied on Libya over the Tripoli government's war against rebels is delaying delivery of supplies to the embattled population, U.N. aid chief Valerie Amos said on Monday.
The United Nations, the United States and the European Union have all imposed sanctions on Libya that between them affect dozens of firms and individuals linked to leader Muammar Gaddafi.
"The manner in which sanctions are implemented and monitored is causing serious delays in the arrival of commercial goods," Amos told the U.N. Security Council.
Amos, head of the U.N. Office for the Coordination of Humanitarian Affairs, told reporters one problem was Libya's centralized distribution system for food and other products.
"So if for any reason commercial supplies coming into the country are not able to come in, then it has an impact on that central distribution system and it has an impact on food stocks across the country," she said.
Amos said the rebel-held east of the country had enough food stocks for about two months, while the west had sufficient stocks for about three months.
In her address to the council, Amos called for all parties to agree a temporary pause in the conflict in the coastal city of Misrata -- a rebel stronghold that has been attacked for weeks by Gaddafi's forces -- and elsewhere.
She said that would enable those who wished to leave to do so. An independent assessment of the humanitarian situation could be made, relief supplies delivered, and third country nationals and the sick and wounded could be evacuated.
She said indiscriminate shelling and bombing by any party and the use of cluster munitions was unacceptable. "It should stop. I don't care who's doing it," she told reporters.
Amos also told the council that military assets should only be used as a last resort to deliver humanitarian supplies and that "we have not yet reached that point." She said later the use of military assets "can seriously compromise the neutrality and independence and security of humanitarian workers."
More than 746,000 people had fled Libya since fighting started in February, she said, and about 5,000 people remained stranded at border points in Egypt, Tunisia and Niger. (Reporting by Patrick Worsnip; Editing by Christopher Wilson)
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