"The law of the United States is quite clear," USATF chief executive officer Craig Masback said during a teleconference.

"It says that unless someone has received a full due-process hearing and found to be ineligible, they must be allowed to compete.

"We do not intend to prevent them from competing in the trials."

Montgomery, Olympic 400 metre silver medallist Alvin Harrison, former world indoor 200 metre champion Michelle Collins and former Olympic relay medallist Chrystie Gaines have been charged by the U.S. Anti-Doping Agency (USADA) with doping offences.

None has failed a doping test.

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The charges are part of an investigation into BALCO (Bay Area Laboratory Co-operative), whose owners face charges of distributing drugs, including the designer steroid THG (tetrahydrogestrinone), to top-class sportsmen and women.

World indoor 1,500-metre record holder Regina Jacobs failed a test for the previously undetectable THG, while Olympic 4x400-metre relay gold medallist Calvin Harrison tested positive for the stimulant modafinil, the U.S. Olympic Committee (USOC) announced in January.

All are awaiting hearings on the charges.

Until those hearings, the six athletes remain eligible to compete for a spot on the U.S. Olympic team.

The team will be chosen during the American trials, which begin on Friday in Sacramento and end on July 18.

The top three in each event will be eligible for the U.S. team, provided they have met Olympic qualifying standards.

Under current policy, USATF will submit four names in each event to the U.S. Olympic Committee (USOC) by July 19 for certification. The USOC must submit its roster for all sports to the International Olympic Committee (IOC) by July 21.

It will then be up to the IOC and, in the case of athletics, the IAAF to determine who will be allowed to compete in Athens.