Citing unnamed counter-terrorism officials, the Washington Post newspaper said on Wednesday that the number had more than quadrupled since the fall of 2003.
The list kept by the National Counterterrorism Centre, NCTC, contains a far greater number of international terrorist suspects and associated names in a single government database than has previously been disclosed, according to the report.
The paper said because the same person may appear under different spellings or aliases, the true number of separate individuals was estimated to be more than 200,000.
US citizens make up "only a very, very small fraction" of that number, The Post said, quoting an administration official, who spoke on condition of anonymity.
An NCTC official refused to say how many on the list - put together from reports supplied by the CIA, FBI, the National Security Agency, NSA, and other offices - were US citizens, the paper said.
"The vast majority are non-US persons and do not live in the US"
The paper quoted him as saying: "The vast majority are non-US persons and do not live in the US."
The NSA is a key provider of information for the database, although officials refused to say how many names on the list are linked to the agency's controversial domestic eavesdropping effort, according to the report.
Under the programme, the NSA has conducted wiretaps on an unknown number of US citizens without warrants.