Five OPEC oil ministers agreed Saturday to call two special meetings later this month to consider ways of halting the decline in oil prices, according to the cartel's Nigerian president. The ministers, at the end of a full day of closed-door meetings, made no recommendations for immediate OPEC action to combat the slipping prices, said Nigeria's Rilwanu Lukman, who was chairman of the session. He said he and the oil ministers of Saudi Arabia, Algeria, Venezuela and Indonesia would invite at least seven non-OPEC oil producing nations to meet with them in Vienna on April 23 to discuss ways of cooperating to stabilize oil prices. Lukman declined to identify the non-OPEC countries, but industry sources said they would be Mexico, Egypt, Oman, Angola, Brunei, Malaysia and Colombia. When asked, Lukman said he would not rule out inviting representatives also from the Soviet Union and Norway. The Soviets are the world's largest oil producers. Oil ministers of all 13 members of the Organization of Petroleum Exporting Countries will then meet in Vienna on April 25, Lukman said. He suggested that the non-OPEC representatives might be asked to attend that session as official observers. OPEC had not previously planned to hold any meetings until its regularly scheduled summer conference June 8. Lukman said the five ministers had decided that special meetings were needed to ``look into the situation generally in the market'' and to consider ways of cooperating with non-OPEC countries. OPEC oil ministers held two meetings with representatives of Mexico, Angola, Egypt, Malaysia, Oman and Brunei in the spring of 1986, but the cartel was unsuccessful in persuading those countries to reduce their production. This time the situation is different, according to Lukman. ``Non-OPEC (countries) have, on their own, realized the need to cooperate'' among themselves and with OPEC, Lukman told reporters after the meeting. OPEC often has declared in recent years that it alone cannot be expected to bear the burden of cutting production in order to stablize oil prices. OPEC controls only about 35 percent of the total world oil supply, down from more than 60 percent in the late 1970s. Lukman said the separate April 25 meeting of all 13 OPEC members was called because of the severity of the recent price decline. ``The price is not what we expected it to be'' after having decided last December to maintain strict oil production limits, he said. Oil prices in the open market are at least $3 below OPEC's official target level of $18 a barrel. Lukman said Saturday's meeting had made no recommendation about whether OPEC should reduce its production, either unilaterally or jointly with non-OPEC producers, as a way of boosting prices. He said increased production by non-OPEC producers this year was partly responsible for the oil price slump. Although Iran was not invited to Saturday's meeting, its deputy oil minister, Kazempour Ardebili, flew to Vienna and met separately with members of the group. He said later in an interview in his hotel room that Iran had proposed that OPEC cut its production by at least 5 percent immediately. He said this should be done with or without parallel action by non-OPEC oil-producing countries. Ardebili accused some OPEC members, which he did not name, of sabotaging Iranian initiatives to boost prices by cutting output. His comments appeared to be directed at Saudi Arabia, an opponent of further cuts in OPEC's share of the world oil market. Persian Iran has been at war with Arab Iraq since September 1980, and Iran often accuses other Arab countries of supporting Iraq directly or indirectly in the conflict. Both Iran and Iraq count on revenues from oil exports to help finance their war efforts.