LAREDO, Tex.  When one of the most successful coaches in the history of track and field goes on trial next month in the long-running federal investigation into doping in sports, lawyers for both sides are prepared to reveal that cheating in track is far more widespread than previously known.

The main witness against the coach, Trevor Graham, has said he supplied illicit drugs and advice on their use to Mr. Graham and his camp of elite athletes, including Marion Jones, as well as to many other sprinters and their coaches.

Angel Guillermo Heredia is identified as Source A in the felony indictment. He agreed to be a cooperating witness three years ago when, according to court filings, investigators confronted him with evidence of his drug trafficking and money laundering. Since then, Mr. Heredia said, he has provided prosecutors with documentation and with the names of many elite track athletes and Olympic medal winners.

Mr. Graham, who is charged with three counts of making false statements to federal agents, says that he is innocent. A defense motion to dismiss, which was denied, said the government’s case had been built on accusations by Mr. Heredia that “are not true and are merely an effort to attempt to divert attention from his illicit drug dealing and the illicit drug usage by athletes.”