A second group joined them two days later, the report said.
The newspaper cites military sources saying the operation began in the southern Syrian region of Deraa.
DEBKAfile, an Israeli website, also reported that up to 250 US-trained rebels entered an area of Syria near the Israeli border this past Saturday and were joined by an additional 300 on Monday.
The US troops and intelligence officers reportedly made their way into Syria a few days before reports emerged that hundreds of men, women and children were killed by an alleged chemical weapons attack in the suburbs of Damascus.
The alleged chemical attack, which some experts argue was suspicious, prompted the United States and other Western courtiers to call for a military response.
US officials said Thursday that the Pentagon was refining its military options for possible strikes on a number of government and military installations in Syria, the Wall Street Journal reported.
Syria's foreign-backed opposition claimed on Wednesday that around 1,300 people were killed in a government chemical attack on militant strongholds in the Damascus suburbs of Ain Tarma, Zamalka and Jobar.
The Syrian government and the army categorically denied any role in the alleged chemical attack.