A. Daniel O'Neal announced yesterday that he won't seek reappointment to the Interstate Commerce Commission when his term expires Dec. 31.

Chairman of the ICC since April 1977, O'Neal has spearheaded ICC moves to reduce some regulatory restraints on the trucking and railroad industries. He has been a member of the commission since April 1973.

In a memorandum distributed to commission members and top staff officials yesterday, O'Neal said he had notified the White House that he doesn't wish to be considered for reappointment, but intends to serve out his term.

O'Neal said he has no plans at the moment but has been talking with friends "very generally" about options available to him. "I have not talked to anyone about any specific jobs," he said. A lawyer, he plans to explore possibilities at law firms, he said. "I'm going into the private world and seek a private income of some kind."

He said he notified the White House this far in advance in hopes the administration will designate someone soon "so we could have an orderly transition."

Although no one from the White House could be reached for comment, sources on Capitol Hill say Darius W. Gaskins Jr. is the apparent favorite to succeed O'Neal. Gaskins was one of three new ICC members who all favor a reduction in regulations.