Oil ministers of the Organization of Petroleum Exporting Countries open their twice-yearly conference here Thursday to plot a production strategy aimed at propping up crude-oil prices at current levels for the remainder of the year.

The ministers of Venezuela, Algeria and Ecuador predicted the meeting would leave prices unchanged and would reaffirm the cartel's recent production cutbacks and output ceiling of 17.5 million barrels a day.

Saudi Arabian Oil Minister Sheik Ahmed Zaki Yamani indicated the meeting would discuss raising the ceiling to make room for an expected increase in demand. He said prices would not change.

The ceiling and accompanying production cutbacks--which have lowered OPEC output by about 5 percent to 17 million barrels a day, according to industry sources--were adopted in March and have done much to dry up the world petroleum glut. The measures staved off a collapse in OPEC prices that had been widely predicted in February and March, and helped spur an upturn in the past month of a penny or more a gallon in prices paid for gasoline by American motorists.

The meeting is expected to serve the psychological purpose of providing an opportunity for OPEC members to recommit themselves to the individual production quotas and $34-a-barrel price structure that they pledged in March to uphold, according to U.S. oil industry executives and Department of Energy specialists.

The temptation is strong for members to offer under-the-counter price discounts to boost sales and thus raise their oil revenues. Iran is openly flouting the agreement, and industry sources say Libya and possibly Nigeria are discounting their prices privately.

"The sky looks a little brighter for OPEC , but there are still a few overhanging clouds that we have to watch carefully," Indonesian Oil Minister Subroto told reporters on his arrival at the luxury hotel where the meeting will take place.

The cartel is essentially playing a waiting game on the assumption--shared by the Americans--that demand for OPEC oil will rise during the second half of this year and further strengthen the cartel's position. The revival would allow OPEC countries to produce more later this year but was not likely to be strong enough to let OPEC jack up its prices, ministers acknowledged.

"We will not move prices this year for sure," Venezuelan Minister Humberto Calderon Berti said.

Saudi Arabia, the world's largest oil exporter and dominant force within OPEC, has pressed the production cutbacks and provided the biggest reduction in its maximum output quota--by 500,000 barrels a day to 7 million barrel a day. Yamani said April production for Saudi Arabia was 6.5 million barrels a day.

The Saudis, determined to safeguard OPEC's role in the world oil industry, also provided support in other ways. They threatened to halt sales to companies that were pressing Nigeria to lower its price and provided the largest share of a $1 billion OPEC loan offered to Nigeria to help it pay bills while waiting for demand to return for its oil.

In another example of OPEC members helping their own, Venezuela recently agreed to buy a substantial amount of Ecuadoran crude, refine it and sell the products. Buyers had been shunning Ecuadoran crude at the official price of $34.25, forcing it to sell some at lower prices on the spot, or noncontract, market. Ecuador and Gabon are OPEC's two smallest producers.

The decisions at the March meeting in Vienna have had a strong effect on the spot markets, where prices have risen from $28 a barrel for Arab light crude--the oil used by OPEC as a benchmark for setting prices--to about 50 cents below the official $34 price.

A four-nation OPEC market-watching committee met yesterday in Caracas, Venezuela, and reported that OPEC production, responding to increased demand, was expected to rise to 19.4 million barrels a day in the third quarter of this year and to 22 million in the fourth--a total increase of about 5 million barrels a day.

Department of Energy specialists say those figures are optimistic and predict output of 19 million barrels and 20.7 million for those periods.

The anticipated recovery in demand may fail to materialize if oil companies decide interest rates are too high to finance rebuilding their inventories or if the U.S. economy continues to stagnate.