* Ministers debate whether compliance would be enough
* IEA, OPEC revise downwards oil demand forecasts
* Inventory levels are high
* Global economic weakness overshadows talks
(Updates with Obama call to Saudi king)
By Henrique Almeida and David Sheppard
VIENNA, March 13 (Reuters) - A feeble world economy and a firmer oil price could persuade OPEC ministers meeting at the weekend in Vienna they should stick to their existing supply targets for now, rather than cut output more aggressively.
On arrival ahead of Sunday's talks, ministers said they were worried about bulging inventories and the impact of economic slowdown on fuel use, but were cautious about demanding action.
"We need to discuss how to drain inventories. We need to evaluate demand and see if it is necessary to take additional measures," Venezuelan Minister of Energy and Petroleum Rafael Ramirez told reporters.
"We have to analyse very carefully the economic situation world-wide ... It is worse than anybody thought it would be. We have a bad situation with demand, demand is destroyed."
Venezuela in the past has been among the first to urge fellow OPEC members to drive the oil price higher.
Both the Organization of the Petroleum Exporting Countries and the International Energy Agency revised down their forecasts for global demand, reflecting the impact of lower economic output on energy demand, in monthly reports released on Friday.
The IEA forecast 2009 oil consumption would shrink by 1.25 million barrels per day (bpd) year-on-year to 84.4 million bpd, while OPEC in its monthly report predicted a contraction of one million bpd to an average of 84.61 million bpd.
Even with the lower demand, the IEA, which represents consumer interests, said full compliance with curbs OPEC has already agreed would be enough to take the group's output a hefty 1.6 million bpd below 2009 demand for its oil.
OPEC's biggest and most influential member Saudi Arabia has yet to comment publicly.
Sources have said the kingdom, which has delivered the largest share of cuts so far, has emphasised the need for tighter compliance from other members of the group.
Analysts have also said that although it would seek a balanced oil market, it would be mindful of the global economy, especially before a meeting of the Group of 20 developed and emerging nations in London in April to seek solutions to the financial crisis.
Potentially adding to political pressure, U.S. President Barack Obama, leader of the biggest energy consuming nation, called King Abdullah of Saudi Arabia on Friday, the White House said, without giving details of the call.
DEEP CUTS
Since September, OPEC has already agreed cuts totalling 4.2 million bpd. They equate to about 5 percent of daily demand and are the deepest and most rapid yet.
Compliance with those targets is historically high at around 80 percent, independent observers have said.
Inventory levels are also high and according to the IEA represent 58.7 days of forward cover -- much more than the 52 days OPEC considers comfortable.
But oil prices have firmed. On Friday, U.S. crude traded around $46, well above a low of $32.40 hit in December, although more than $100 below last year's record high.
The IEA has warned prices could eventually race back up to record levels as reduced profit margins limited investment in new oil production. What the world economy needed at the moment, however, was the stimulus provided by cheaper oil, it said.
"We think that OPEC's existing targets will probably begin to tighten the market quite sharply from late in the second quarter onwards," said David Fyfe of the IEA's oil industry and markets division.
"And therefore OPEC cuts are already putting a floor under the price. What we probably don't need at the moment in this current short-term weak economic environment is a sudden surge in prices if OPEC were to decide to go even further on Sunday."
For related graphic, showing the relationship between OPEC output cuts and the oil price, please click on:
https://customers.reuters.com/d/graphics/OL_OPEV0309.gif (For a factbox on past OPEC production changes)
(Additional reporting by Alex Lawler, Simon Webb and Sarah Marsh in Vienna and Jane Grieve and Christopher Johnson in London, Writing by Barbara Lewis; editing by William Hardy)