Dr Zaki Badawi, head of the Muslim College, said he was denied entry when he arrived in New York on Wednesday. No explanation was given, he said.
He had been invited to speak at the Chautauqua Institution in Chautauqua, New York, where he planned to give a talk under the title The Law and Religion in Society.
A spokeswoman for the Customs and Border Protection office in New York said when Badawi's flight from London to John F Kennedy International Airport landed on Wednesday, customs agents had information that showed he was "inadmissible".
Badawi then voluntarily withdrew his application for entry into the country, said the spokeswoman, Janet Rapaport. She said privacy rules prevented her from disclosing the specific information that was used to bar Badawi and said she did not know what database the information came from.
She also said she did not know if last week's bombings in London had anything to do with barring Badawi.
A federal security official said Badawi was named on a US terror watch list, but provided no further detail. The official spoke on condition of anonymity.
"The people I was speaking to were very junior people, and they are just executing things they were told"
Dr Zaki Badawi
The US Embassy in London did not immediately respond to a request for comment.
No explanation was given for his exclusion, Badawi said in a telephone interview. "The people I was speaking to were very junior people, and they are just executing things they were told," Badawi said.
"They were very very embarrassed, and I felt sorry for them."
Badawi said he had visited the US many times before, the last time in 2003.
On Sunday, Badawi joined other British religious leaders in condemning the bus and subway bombings.
He appeared with the Archbishop of Canterbury, Rowan Williams, the Roman Catholic Archbishop of Westminster, Cardinal Cormac Murphy O'Connor, Free Churches Moderator David Coffey and Chief Rabbi Sir Jonathan Sacks.
Azim Nanji, director of the Institute of Ismaili Studies in London and a participant in the Chatauqua conference, said he was "deeply saddened" by the exclusion of a "moderate voice".
"I felt it was very important that Americans should hear, particularly at this time, a voice from a leading British Muslim who is well respected by the British government, somebody they turn to for advice," Nanji said.
"Inviting the Dr Badawis of the world into that conversation is crucial," said Eboo Papel, founder and executive director of the Chicago-based Interfaith Youth Core, who said he had come to hear Badawi.
"It's clear that a large segment of the Muslim community wants to be in a positive relationship with Western societies," Papel said.
Last year another UK Muslim,
Yusuf Islam, was denied entry
"When representatives of that segment, people who have been knighted by the queen and are close advisers to the government, are rejected, it hurts our efforts at building multifaith societies and it gives grist to extremist Muslims who say, 'See, the West is against Islam, period".
Tom Becker, president of the Chautauqua Institution south of Buffalo in western New York, said he did not know why Badawi was barred. "Whatever it was some kind of misinterpretation of something," he said.
Badawi was given an honorary knighthood and in 2003 he was among the guests of Queen Elizabeth II at a state banquet for US President George Bush.
Badawi said he was detained for about six hours. "America is a lovely country. There is no reason why it should behave like that," Badawi said.
In September, Yusuf Islam, formerly known as Cat Stevens, was ejected from the US without explanation. Islam's flight from London was forced to make an emergency landing in Maine when US authorities discovered he was aboard.