MANDAN, N.D. (AP) _ Six teachers who were notified their contracts may not be renewed were presented with a postage-due bill of $1.25 to hear the bad news, a school official said Monday.

Mandan School Superintendent Pius Lacher said the postage due resulted from a secretary's error when the letters were mailed special delivery last week.

The secretary paid a special delivery rate of $1.67 on each letter, without knowing it only assured immediate delivery to the address and not to the person, Lacher said. Delivery to a person is ''restricted'' mail and requires an additional $1.25, he said.

Lacher said two teachers refused to pay, and the letters were returned to the school. The four who paid were immediately reimbursed, he said.