(Recasts, adds Ahmadinejad quote in paragraph 5)

By Souhail Karam and Simon Webb

RIYADH, Nov 18 (Reuters) - An OPEC summit ended on Sunday in sharp political division over whether to take action over the weak dollar, as heads of state vowed to keep providing Western consumers with an "adequate" supply of oil.

A fall in the value of the U.S. dollar on global markets helped fuel oil's rally to a record $98.62 on Nov 7 -- causing Western consumer nations to call for more OPEC supplies to cool prices -- but it has also eroded the purchasing power of OPEC members.

The final statement of the oil cartel's summit in Riyadh did not include any reference to the dollar's predicament, in an apparent victory for U.S.-allied moderates led by Saudi Arabia.

But Iran and Venezuela -- anti-U.S. firebrands locked in tough diplomatic disputes with Washington -- made clear before and after the summit that they would press for action, which could include pricing oil in a basket of currencies.

Such a move would be a political blow to the United States, whose currency Iran's President Mahmoud Ahmadinejad told reporters had become a "worthless piece of paper."

Fears the United States or its ally Israel could attack Iran -- over a nuclear energy program Washington says is a cover for seeking atomic weapons -- have helped drive world oil prices to record levels. Tehran denies the charge.

Iraqi Finance Minister Bayan Jabor told Reuters after the summit's close that, backed by Ecuador, the anti-U.S. powers won agreement that finance ministers would discuss the issue before a scheduled oil ministers meeting in Abu Dhabi on Dec. 5.