An FBI informer who was one of Labor Secretary Raymond J. Donovan's unidentified accusers has pleaded guilty to a single count of lying to FBI agents during a 1982 investigation of alleged ties between Donovan and organized crime.

Justice Department prosecutors, in turn, dropped charges stemming from a series of other statements that the informer, Michael Klepfer, an executive of Canny Trucking Co. of Binghamton, N.Y., allegedly made to FBI investigators.

Klepfer pleaded guilty Friday in U.S. District Court in Syracuse to a one-count information for falsely claiming that the Teamsters union had funneled $20 million into President Reagan's 1980 presidential campaign through Donovan and that Donovan was supposed to reciprocate by making "certain recommendations with regard to official governmental matters at the end of President Reagan's first term in office."

The original indictment, which was more detailed, charged that Klepfer had claimed that the alleged arrangement was the reason for the murder of Fred Furino, who once worked at Canny Trucking's Elizabeth, N.J., terminal. Furino, who allegedly served as a sometime "bagman" for New Jersey mobsters, was found dead in the trunk of his car in New York City on June 11, 1982.

According to the indictment, Klepfer subsequently told FBI agents that Furino was killed to keep him from telling federal authorities about the purported $20 million scheme, which allegedly was devised to obtain presidential pardons for two imprisoned felons, organized crime boss Russell Bufalino and former Teamsters official Anthony (Tony Pro) Provenzano.

Originally indicted on charges of obstructing justice and three counts of lying to FBI agents, Klepfer is scheduled to be sentenced in January.

Prosecutor Douglas Grover said he considered the case's disposition "fair" in light of the penalty Klepfer faces and his "admission that he misled the FBI." Klepfer's attorney, Sal Cognetti Jr., denied that it amounted to a tacit admission of the other alleged misstatements in the original indictment.

"We pled not guilty to those," he said, "and that means just what it says, 'not guilty.' "