VIENNA, AUG. 28 -- OPEC has postponed the meetings of two ministerial committees set up to monitor world oil prices and production from the cartel's 13 member nations until Sept. 10 from Sept. 7, the OPEC news agency reported today.

The agency, OPECNA, quoted an unidentified official at the OPEC Secretariat in announcing the new date for the committee meetings. No reason was given for the postponement.

OPEC President Rilwanu Lukman called the meetings Tuesday after oil prices plummeted by more than $1 a barrel Monday on a report by the Middle East Economic Survey (MEES) that the 13-nation cartel was exceeding its self-imposed production ceiling by 3 million barrels a day. The authoritative oil journal has close ties to OPEC.

Oil traded on world markets had fallen by about $4 a barrel since mid-July amid growing concern over OPEC's surplus production, until Lukman convened the committees in a move that reversed the price slide.

Lukman, who also is Nigeria's oil minister, told a news conference in Lagos Tuesday the Organization of Petroleum Exporting Countries would take all "necessary measures" to stabilize the world oil market. He did not elaborate.

OPEC established the two committees to enforce its June 27 agreement to limit production to 16.6 million barrels a day for the second half of the year in order to defend its $18-a-barrel benchmark price.

At the June meeting OPEC set up the three-man ministerial committee to visit member states and to motivate them to stay within their individual output quotas alloted under the cartel's production ceiling. Lukman and the oil ministers of Venezuela and Indonesia are on the ministerial committee.

MEES, which is based in Nicosia, Cyprus, said OPEC was producing 19.7 million barrels a day in August, with the bulk of the surplus production coming from the group's Persian Gulf states.

OPEC created another committee to monitor world oil prices levels and named the oil ministers of Nigeria, Venezuela, Indonesia, Saudi Arabia and Algeria to this panel.

At its June ministerial summit OPEC said the pricing committee would have the power to call a full emergency meeting of all 13 members if world oil prices deviated "significantly" from its benchmark price