AIRO, Sept. 18 ・Sometimes shouting, sometimes crying, sometimes shaking his head, Mohammed al-Amir Atta said today that his son and namesake was a shy man who could not possibly have sent a hijacked jet slicing through the first World Trade Center tower.

"Mohamed. Oh God! He is so decent, so shy and tender," said the father, a 65-year-old retired lawyer. "He was so gentle. I used to tell him, `Toughen up, boy!' "

Mr. Atta stood on the concrete doorstep of his 11th-floor Cairo apartment today, alternating between rage at the picture being painted of his son as one of the attack's ringleaders and pride that his boy had done well abroad after graduating with average marks in architecture from Cairo University.

The elder Mr. Atta laced his conversation with fierce attacks against the United States, blasting it repeatedly for supporting Israel and for moral contagions like adultery and homosexual marriage.

Some of his son's university friends in Germany have described Mohamed Atta as a sharply intelligent, strict, serious man who seemed to retreat socially, seeking solace from religion.

The elder Mr. Atta said he never encouraged his children to be social, even avoiding the frequent contact between relatives so common in Egypt. Neighbors in their slightly tattered, middle-class neighborhood in Giza, just off the road to the Pyramids, confirmed that family members rarely said more than hello.

"We keep our doors closed," Mr. Atta said, "and that is why my two daughters and my son are academically and morally excellent."

He was outraged at reports that his son was seen drinking in a Florida bar on the eve of the attacks.

"My son is a hijacker and drinks vodka!" yelled Mr. Atta, his face reddening to the roots of his white hair and his hands waving. "It is like accusing a decent, veiled religious girl of smuggling prostitutes into Egypt. It is nonsense, imagination!"

Indeed, two German students who spent from August to October 1995 in Cairo with Mr. Atta while completing an urban renewal field study said they did not drink alcohol near him because it made him uncomfortable.

The elder Mr. Atta said that while his son was religious, that fervor did not extend to politics.

"He was a donkey when it came to politics," his father said. "I advised him, like my father advised me, that politics equals hypocrisy."

The father said the only vaguely political remark he heard his son make was that the restoration of a mosque in Cairo's old city was too lavish, and the money could be better spent on job creation.

But the two German classmates, Volker Hauth and Ralph Bodenstein, said that Mr. Atta, who left Egypt in 1993, spoke with increasing bitterness about what he saw as the autocratic government of President Hosni Mubarak and the small coterie of former army officers and of rich Egyptians gathered around him. The classmates said he called the ruling elite "the fat cats" and decried both their close ties to the United States and their suppression of religious and nongovernmental organizations.

The entire restoration project around the old city gates, Bab al Nasr and Bab al Futuh, involved knocking down the homes and workshops of the poor. "It made him angry, he said it was a completely absurd way of developing the city, to try to make Disney World out of it," said Mr. Bodenstein, interviewed by telephone.

Mr. Atta said he did not know many details of his son's life in the United States, other than that he thought he was going there for more education. The younger man was last in Egypt a year ago.

If he was on the plane, and there were books left in a suitcase about flying, it was because he had a curious mind, the father said. Someone like Israel's intelligence agency had the capacity to organize such an attack, the father said. But his son, an urban planning architect, did not.

"I do not believe my son did it; I am sure he is alive," the father said. "He was afraid of flying."