Pointing toward other potential terrorist threats, the Justice Department says that about 20 people have been charged since the Sept. 11 attacks with fraudulently obtaining licenses to transport hazardous materials.

Declaring that terrorism ``is a clear and present danger to Americans today,'' Attorney General John Ashcroft said Tuesday that some people who sought such licenses may have links to the hijackers of the four planes that crashed in New York, Washington and Pennsylvania, killing thousands.

``Intelligence information available to the FBI indicates a potential for additional terrorist incidents,'' the attorney general told Congress.

Since the attacks, about 20 people have been charged with fraudulently obtaining licenses to transport hazardous material, said a senior Justice Department official, who spoke on condition of anonymity. He declined to elaborate.

Nabil Al-Marabh, 34, a former Boston cab driver taken into custody in Chicago last week by investigators, holds a commercial driver's license and is certified to transport hazardous materials. Al-Marabh has been moved to New York for questioning.

The focus on trucks with hazardous materials follows disclosures that Mohamed Atta, suspected of piloting one of the two hijacked passenger airliners that struck the World Trade Center, was interested in farm crop-dusting planes. Ashcroft said the FBI had gathered information raising fears that agricultural aircraft could be used in a biological or chemical attack.

A convicted terrorist collaborator testified just two months ago about another potential threat, saying in court that he trained for a chemical attack at a camp inside Afghanistan where poison was unleashed to kill dogs.

``In regard to targets in general ... we were speaking about America,'' Ahmed Ressam testified in July. Ressam said terrorist trainers discussed dispensing poison through the air intake vents of buildings to ensure the maximum amount of casualties.

In the probe of the Sept. 11 attacks, the FBI is investigating whether some of the hijackers who destroyed the World Trade Center practiced their approaches by renting small planes at New Jersey flight schools and flying along the Hudson River toward the twin towers.

In France, anti-terrorist police detained at least four people early Tuesday in connection with a planned attack on the U.S. Embassy in Paris and other U.S. interests in France. Seven people already were in custody in France in connection with the alleged plot.

In other developments:

—The FBI released a Saudi doctor living in Texas who had been taken into custody and brought to New York for questioning earlier in the investigation. Al-Badr Al-Hazmi, a radiologist whose name was similar to two of the 19 hijackers, returned to San Antonio after nearly two weeks in custody as a material witness — someone believed to have important information about the investigation.

A law enforcement source, who spoke only on condition of anonymity, said authorities questioned the doctor about whether his credit card may have been stolen by the hijackers or their associates.

—A Saudi man arrested 13 miles south of Washington Dulles International Airport the night after the terrorist attacks passed an FBI-administered polygraph test and faces only an immigration-related charge, his attorney said. Drew Hutcheson said Khalid al-Draibi was cleared by the FBI after being asked whether he had any involvement in the attacks or whether he knew anything about them in advance.

—Three men in San Diego who authorities believe knew some of the suspects in the Sept. 11 attacks have been detained as material witnesses and could be sent to testify before a grand jury in New York, a law enforcement official said.

—In Arkansas, one of five people stopped for speeding has a name that is on the FBI's list of people it wants to talk to in the investigation, said Cross County Sheriff Ronnie Baldwin. All five were detained at the FBI's request.