The chairman of the North Carolina Republican Party and one of the state’s leading political donors together sought to use campaign contributions to bribe the state’s insurance commissioner, federal prosecutors said in an indictment that was unsealed on Tuesday.

The 23-page indictment — detailed with accounts of clandestine airport meetings and promises of millions of dollars in illicit donations — intensified the political tumult in a state already roiled by partisan warfare and a fraud-tainted congressional election. And it also showed how, at least in the judgment of prosecutors, a leading political operative and one of his most important benefactors tried to shape government oversight in one of the nation’s largest states.

“These men crossed the line from fund-raising to felonies when they devised a plan to use their connections to a political party to attempt to influence the operations and policies of the North Carolina Department of Insurance,” said John A. Strong, the special agent in charge of the F.B.I. office in Charlotte, N.C.

The party chairman, Robin Hayes, faces the gravest set of charges of the four men who were indicted. Mr. Hayes was accused of bribery and conspiracy to commit honest services wire fraud, along with several counts of making false statements. Three other people, including Greg E. Lindberg, the chairman of an investment firm in Durham and a prolific Republican contributor, were also charged.