An article in the Sept. 17 Business & Financial section should have said that an injunction against Conoco was the third the Federal Energy Regulatory Commission had obtained. It also should have said that Mobil would pay a refund of $18 million as part of another injunction included in a settlement that is being appealed.

Conoco Inc. has been ordered by the Federal Energy Regulatory Commission to refund at least $600,000 to pipeline customers for overcharges for natural gas.

The refunds were part of a settlement with the oil company in which Conoco consented to an injunction prohibiting it from failing to comply with such orders.

FERC charged in a complaint filed as part of the settlement that Conoco had committed 65 violations of the Natural Gas Act or of the commission's refund orders. But, as part of the settlement agreement, the complaint did not spell out what the violations were.

Conoco neither admitted nor denied the allegations. Action on the complaint ended with the injunction against Conoco.

The injunction, approved by Judge Gabriele K. McDonald of the U.S. District Court for the Southern District of Texas, is only the third time in its history that FERC has sought an injunction, according to a FERC spokeswoman. The commission has, however, ordered larger refunds, including an $80 million refund that Mobil Oil Corp. was ordered to make in May 1980.

The commission found that Conoco's charges to some customers had exceeded levels that FERC deemed just and reasonable and ordered Conoco to make refunds. El Paso Natural Gas, which will receive $413,900, is in line for the bulk of the refunds.