WASHINGTON — The FBI has begun investigating whether Roger Clemens lied to Congress when he denied taking steroids, officials said today in the case of another baseball star snared in a long-running inquiry into drug use by professional athletes.

Clemens, the All-Star pitcher and seven-time Cy Young Award winner, maintains he has never used steroids or other performance-enhancing drugs. His former personal trainer, Brian McNamee, claims otherwise, testifying that he injected Clemens with human grown hormones and steroids at least 16 to 21 times from 1998 to 2001.

FBI agents in Washington opened the case a little more than two weeks after both Clemens and McNamee appeared at the same House hearing on Feb. 13, each accusing the other of lying. Three law enforcement officials, speaking on condition of anonymity because of the sensitivity of the case, confirmed the inquiry had begun.