Former Gulf Oil Corp. lobbyist Claude C. Wild Jr. pleaded guilty yesterday to a misdemeanor charge of making an illegal contribution to the 1972 Senate campaign of Sam Nunn (D-Ga.).

Wild's plea, which exposes him to a maximum possible jail term of one year and fine of $1,000 at a sentencing date to be announced later, ends more than 18 months of litigation over his disbursement of Gulf's cash to various political campaigns.

Wild was indicted in March, 1976, on charges of making an illegal cash contribution of $5,000 to the campaign of Sen. Daniel K. Inouye (D-Hawaii), and a contribution of $2,500 to Nunn's campaign. U.S. District Court Judge Joseph C. Waddy dismissed the count involving Nunn, however, and later acquitted Wild of the count involving Inouye.

The government appealed the dismissal of the Nunn count and the U.S. Court of Appeals ordered it reinstated. Wild was scheduled to go to trial on the felony count involving Nunn when he agreed to plead guilty to a misdemeanor count involving the same contribution.

In his plea before Judge Waddy yesterday, Wild said he was "reluctantly" admitting his guilt to making the illegal contribution through a Gulf associate to an Atlanta businessman for Nunn's campaign.