WASHINGTON, JANUARY 27 Khalid Shaikh Mohammed, suspected mastermind of the 9/11 plot, obtained a visa to come to the US just weeks before the attacks despite being under a federal terrorism indictment, a report by the federal commission investigating the attacks revealed on Monday.

As many as eight of the hijackers entered the US with doctored passports that contained ‘‘clues to their association’’ with Al Qaeda that should have been caught by immigration authorities, commission investigators said.

The newly disclosed findings challenge previous claims by top CIA and FBI officials that the hijackers’ records and paperwork were so clean that they could not have aroused suspicion. The commission also heard testimony from a US customs agent who blocked the entry of a Saudi citizen investigators now believe may have been the intended 20th hijacker.

Authorities later learned that Mohammad Atta, the leader of the attack, was at the Orlando, Florida, airport the same day Mohammed Al-Qahtani, who is in US custody, was stopped. The disclosures were included in the first staff reports to be issued by the commission since it opened its inquiry last year, and came during a day-long hearing devoted to immigration and intelligence-related failures by assorted government agencies.

Also on Monday, President Bush identified an Al Qaeda operative caught in Iraq 12 days ago as a senior official in the organisation who had close ties to Mohammed. Bush said Hassan Ghul was captured while in Iraq trying to facilitate attacks by insurgents against US troops. He said Ghul had ‘‘reported directly’’ to Mohammed, the operational commander of Al Qaeda who was captured in Pakistan in March.

Mohammed had obtained a visa to visit the US on July 23, 2001 — about six weeks before the attacks. He applied for visa using a Saudi passport and alias — Abdulrahman al Ghamdi — even though he is Pakistani-born and was not believed to be in Saudi Arabia at the time the application was filed, according to a portion of the staff report read by Susan Ginsburg, senior counsel to the commission. She challenged CIA Director George Tenet’s description of 17 of the 19 hijackers as arriving in the US ‘‘clean’’ of activities that would arouse suspicion.

Some of the most startling details to surface on Monday centered on the case of Qahtani, the Saudi who was turned away by customs officials upon his arrival at Orlando airport on August 4, 2001. The man was screened by Jose Melendez-Perez, an inspector with Customs and Border Protection, now part of the Department of Homeland Security.

Testifying before the commission, Melendez-Perez said he was immediately suspicious of Qahtani, who arrived with no return ticket, spoke little English, behaved menacingly and offered conflicting information on the purpose of his travel.