The U.S. Anti-Doping Agency sent letters to 100-meter world record holder Tim Montgomery and four other track and field athletes notifying them of potential drug violations, according to sources and lawyers with knowledge of the letters.

Letters were delivered by overnight mail yesterday to Montgomery, Ukrainian sprinter Zhanna Pintusevich-Block, U.S. sprinter Chryste Gaines, and U.S. 400-meter runners Michelle Collins and Alvin Harrison, the sources said.

Five-time Olympic medal winner Marion Jones did not receive a letter, but she apparently remains under investigation by USADA officials, who contacted Jones's attorneys yesterday with further questions, according to a Jones spokesman.

USADA has has said it would keep cases open as long as necessary to gather evidence despite the looming July 9-18 U.S. Olympic trials. "If it takes time for relevant information to be received and thoroughly reviewed, we will take that time," said USADA director of legal affairs Travis Tygart.

The cases are unique in that none of the athletes notified of potential charges has tested positive for a banned substance. All are under investigation based on evidence obtained from a federal raid of the Bay Area Laboratory Co-Operative last fall in Burlingame, Calif.

The letters were sent Monday within hours of an unsuccessful last-ditch attempt by USADA to secure an interview with BALCO owner Victor Conte, who was indicted in February on federal steroid distribution charges, according to a source. Conte has pleaded not guilty to charges of distributing designer steroids and banned drugs to athletes.

USADA also sought Conte's cooperation during meetings in December and April, but Conte's lawyers, seeking a plea bargain that would exempt Conte from jail time, have repeatedly rebuffed USADA. Talks between Conte and the Department of Justice collapsed last week.

Tygart declined to comment on Conte, Jones or any specifics pertaining to the investigations. USADA did confirm in a statement that it had sent letters to several athletes as a first step in determining whether doping rules had been violated.

The lengthy letters included dozens of pages of attachments that described the potential charges citing, at least in some cases, evidence of use of a host of banned drugs including testosterone, norbolethone, THG, trenbolone, modafinil and erythropoietin (EPO), according to a source.

Montgomery, who set the 100 world record of 9.78 seconds in 2002, is the most high-profile of the athletes who might face charges. His attorney, Cris Arguedas, has said she has seen no compelling evidence against him from USADA.

In a statement, Jones defended Montgomery, with whom she has an infant son: "Tim Montgomery is a good person, a great athlete and an even better father. I support him and believe in him and I have no doubt that if a fair process is applied that Tim will be racing for Gold in Athens this August."

Pintusevich-Block had the distinction of ending Jones's 54-sprint winning streak in 2001, upsetting her to win the 100 world title that year. She resides in Johnson City, Tenn., with her agent-husband, Mark.

Harrison won a silver medal at the 2000 Summer Games in the 400. Harrison's twin, Calvin, tested positive last year for the stimulant modafinil, but his case has not been resolved.

Gaines, a 2000 Olympian and 2001 outdoor champion in the 100, tested positive for modafinil last year and received a warning. Her coach is Remy Korchemny, one of four men indicted in the BALCO case.

Collins was the world and indoor champion in the 200 last year. Her attorney, Brian Getz, previously has said she would vigorously contest any charges and would try to take the matter to the U.S. courts if Collins were charged and lost in USADA's arbitration system.

USADA, which will decide whether to press forward on the cases based on recommendations from its internal review board, stated in the letters that it will expedite its customary 40-day period between notifications and hearings in an attempt to resolve the cases before the Olympic trials -- unless the athletes agree to withdraw from consideration for the 2004 Summer Games.

The U.S. athletes have 10 days to respond to the letters in writing to the agency's review board. As per its policy in the cases of international athletes, USADA is required to notify the athlete's national federation and world governing body of track and field (IAAF) of the possible allegations. Pintusevich-Block's case is likely to be handled in Ukraine and overseen by the IAAF.

If USADA formally charges the U.S. athletes, they will be free to compete in the United States pending the resolution of their cases via arbitration. However, the IAAF might use its power to provisionally suspend athletes from international competition, IAAF spokesman Nick Davies said.

Several sources and lawyers said USADA has tried to strong-arm some athletes into cooperation by bringing up their testimony before a federal grand jury last year. The tactic has been used with Gaines, according to Cameron Myler, her attorney. At least some athletes involved in the case admitted to drug violations before the grand jury, several sources said.

Jones, however, has maintained that she has said and done nothing that could be used against her. She has repeatedly said she has been drug-free throughout her career.

USADA's evidence against Jones -- some of which her lawyers received from USADA and made available to the press -- includes a calendar with the initials "MJ" along with unexplained letters that investigators alleged represent different drugs. Jones's lawyer, Joseph Burton, has described the evidence as "not convincing."

Though USADA has secured the cooperation of sprinter Kelli White, who admitted using a variety of drugs and accepted a two-year ban, she might be unable to decode the calendars as a witness for USADA.