OPEC oil ministers agreed today on a shift in strategy that could depress prices further.

The Organization of Petroleum Exporting Countries appointed a six-member committee to work out details of a policy that would abandon rigid official prices, which OPEC has been unable to enforce in a glutted market despite repeated production cuts.

OPEC's 13 members are battling to maintain their share of the market and hope to sell an average of 16 million barrels a day. The group's share of the market in the noncommunist countries has dropped to about 35 percent from 60 percent in 1979.

"We are not willing to lose market share to non-OPEC producers anymore," a senior delegate said.

Algeria's oil minister, Belkacem Nabi, resisted the new strategy in what one delegate described as an angry exchange with Ahmed Zaki Yamani, his Saudi counterpart. Nabi argued that OPEC's rules forbade a policy of charging free-market prices, but Yamani dismissed that view as "theoretical," given that most OPEC crude has been sold below market prices in recent years.

Ministers said that there would be no final decision on details of the new strategy at this meeting, expected to end Monday.

At present, OPEC is producing about 17.5 million to 18.5 million barrels a day, taking advantage of a seasonal rise in demand to exceed its self-imposed ceiling of 16 million.

Venezuela has argued that OPEC should try to cut back to about 16 million barrels a day, but others have called that impossible. Several members producing above their quotas -- such as Iraq, Nigeria and Ecuador -- have said openly that they do not intend to cut back.

"Nigeria has made enough sacrifice to promote the ideals of OPEC," Tamunoemi David-West, the Nigerian minister, said in a press release. Saudi Arabia, which used to take responsibility for the bulk of the output cuts, told other members it no longer would give up a single barrel of its quota of 4.35 million, delegates said.

Some delegates argued that OPEC should produce 18 million or even more. "For the first time I see a mood of being very aggressive," one delegate said. "People are saying, 'Okay, let's show them a lesson,' " a reference to producers outside OPEC, such as Britain and Norway, whose North Sea output has risen in recent years.