The first witness in the Roger Clemens perjury trial was called Wednesday afternoon as the government called Charles W. Johnson, House parliamentarian from 1994 to 2004.

Johnsonis expected to testify about why Congress had the authority to investigate the use of steroids in baseball. Attorneys for both sides presented their opening arguments to the jury earlier Wednesday.

Defense lawyers have signaled that they will argue that Clemens cannot be convicted of obstructing Congress because the House committee overstepped its authority when it held a hearing pitting the pitcher against his trainer.

In essence, the attorneys argue, the hearing was a show trial that had nothing to do with pending legislation of any kind, and Clemens cannot be convicted of obstructing Congress if it was not exercising its “due and proper” power, as alleged in the indictment.

Defense lawyers are also expected to raise questions about whether Clemens’s statements to a House committee were “material” to any congressional action.

The only official action taken by the committee after the hearings was to refer the matter to the Justice Department for a possible perjury prosecution.