OPEC will not achieve its target price of $18 a barrel for crude oil in the first half of 1989, because its planned production ceiling will exceed world demand and cartel members are likely to cheat on their quotas, U.S. oil analysts said.

Saudi Arabia, OPEC's largest oil producer, does not want to see $18-a-barrel oil and will not allow the $18 target to be achieved, said Frank Knuettel of Prudential-Bache Securities Inc.At the Vienna talks of the Organization of Petroleum Exporting Countries that ended in agreement Monday on a total output ceiling of 18.5 million barrels per day, Saudi Arabia proposed that the 13-member cartel defend a price floor of $15 a barrel.

The Saudi plan almost scuttled the pact, which trims the group's production from the estimated 23 million bpd it is now pumping. The accord also reinstated OPEC's reference price of $18 a barrel for a basket of several grades of crude oil.