The rhythms of life here turn upside down during the holy month of Ramadan. Daytime fasting leads to somnolent afternoons, but the real day starts at sunset. After the traditional iftar meal to break their fast, Saudis flock to the streets, offices reopen, life begins again. By 1 a.m., traffic still clogs the highways and customers pack the malls.

At a pizza shop at the glitzy Kingdom Mall, Sinan Dmaitri works the night shift slinging pepperoni pies. It is not where he imagined he would be just a few months ago. His life has been turned upside down, not only by the holy month but by the dramatic deterioration in the way Saudi Arabia and the United States view each other.

Like so many other young Saudis, Dmaitri, 26, has been kicked out of the United States, where he was studying at a junior college in Texas. And like so many other educated, privileged Saudis who once considered America their second home, the suspicion and sometimes hostility directed at his people since Sept. 11, 2001, have left him embittered toward a country he once admired.

"I was thinking about staying there and living my life," Dmaitri said. Now, he said, "I'll never go back, no way."

The souring ties between the United States and Saudi Arabia have generated resentment among the Saudis who once were America's best friends here, the pro-Western slice of society that has exercised U.S.-friendly influence in this conservative Islamic kingdom. Every time a new allegation surfaces, such as the discussion in Washington that money from the Saudi ambassador's wife may have found its way to the Sept. 11 hijackers, the finger seems pointed at them.

Suddenly the people who have spent the most time embracing and defending the United States feel abandoned.

"These are the people who have been carrying the flag here," said Kamal Bahamdan, a Saudi businessman who was educated at Boston University and splits his time between here and his Boston home. "They feel betrayed."

"We are hurt," said Mohamed al-Ghamdi, a journalist who lived and studied in the United States for eight years and can talk nostalgically about Bloomington, Ind. "We don't go to America anymore. We are afraid of you. America is engaged in war and thinks we're responsible."

The estrangement has spread beyond the diplomatic circles where international relations normally play out. It runs from the military officers who no longer train alongside U.S. counterparts to the tourists who no longer visit Florida or Las Vegas to the rich businessmen or princes who no longer check into U.S. hospitals for important medical procedures.

As elsewhere in the Middle East, this has taken an economic toll. But it becomes especially pronounced because of Saudi Arabia's oil-based wealth and historically strong ties to the United States. Business and tourist travel to the United States has plummeted by two-thirds or more in the last year, according to officials on both sides, costing American businesses hundreds of millions of dollars. U.S. exports have dropped by 25 percent from last year, costing the United States at least $1.5 billion. Saudi Arabian Airlines even canceled its weekly flights to Orlando because fewer Saudis are going to Disney World.

"We've scared off a lot of tourism and scared off a lot of medical patients, and the impact on our economy is more substantial than people realize or want to recognize," said Charles Kestenbaum, a commercial officer at the U.S. Embassy here until becoming a corporate consultant last summer. "We're treating all Saudis as if they're terrorists. Our inability to distinguish between who is a friend and an enemy turns everyone into an enemy. It's a self-fulfilling prophecy."

U.S.-Saudi relations trace their history to 1945, when President Franklin D. Roosevelt met with King Abdulaziz ibn Saud, founder of the modern Saudi state, aboard a ship on the Great Bitter Lake in the Suez Canal. That meeting and FDR still hold an almost mythic place in the Saudi national identity.

Despite a harsh turn in relations during the oil crises of the 1970s, the United States helped Saudi Arabia transform itself into a rich, modern state with gleaming buildings, Western stores and many trappings of an American-style consumer culture. So close had the two become that Washington dispatched 500,000 troops to protect the kingdom and expel Iraqi invaders from neighboring Kuwait in 1991.

Masked by all the oil money and high-fashion outlets, however, was a cultural chasm that came into clearer focus after it was revealed that 15 of the 19 Sept. 11 hijackers were Saudis. To American eyes, Saudi Arabia suddenly looked like Afghanistan with money, seemingly a breeding ground for terrorism and promoter of a fundamentalist brand of Islam that subjugates women, who are forced to veil themselves and cannot so much as drive a car.

Less noticed in Washington, though, was the changing view on this side. The United States now looks ungrateful and unwelcoming, so willing to toss aside decades of friendship that it rousts Saudi students from their classrooms, inflicts humiliating interrogations on one-time business partners and ignores slow but steady reforms here.

Stung by what they consider guilt by association, virtually every government official and many educated Saudis recite like a mantra the conclusion that Osama bin Laden, the Saudi-born fugitive, deliberately stocked the Sept. 11 team with Saudis to drive a wedge between the kingdom and the United States.

"I can understand the fear and frustration that exists in the United States after the 9/11 catastrophe," Prince Saud Faisal, the foreign minister, said in an interview. "Had that situation happened here, we would have been just as anxious and just as fearful as they are. But it is during periods of crisis that wisdom is required. . . . Obstacles are being placed not in front of the terrorists or the evildoers, but in front of people who have nothing to do with that. And I think that is the most damaging aspect of the situation."

The crackdown on Saudis traveling to the United States recently escalated.

Last month, the U.S. government began requiring most visiting Saudi men to register and provide fingerprints, photographs and details about their plans upon arrival and departure. Those staying 30 days or longer must submit to interviews and notify the government within 10 days of changing jobs, schools or homes.

The new requirements, effective Oct. 1, put male visitors from Saudi Arabia, Pakistan and Yemen on a list that previously covered those from states designated as sponsors of terrorism, such as Iran, Iraq, Sudan and Libya.

The message, according to many Saudis with U.S. ties, was simple: Stay away. And so they are.

"It's the fear," said Saleh al-Omair, 43, an insurance company manager who spent five years in the United States and graduated from the University of South Florida. "People are fearing they'll be arrested for no reason. Normal people who never talk politics, who have never held a gun in their hands, they're so scared."

Wealthy older Saudis who would fly with large entourages and spend months getting treatment at the Mayo Clinic in Minnesota or the Texas Medical Center in Houston have now begun going to Europe, Canada or China instead.

"It's been very difficult for lots of patients, and I know that patients have stopped having their treatment in the U.S. and have been searching for another place," said Mansoor al-Mansoor, coordinator of the chief executive office at the King Faisal Specialist Hospital and Research Center in Riyadh.

Sinan Dmaitri had been in Texas since 1999 and was studying and managing a T.G.I. Friday's restaurant at the time of the Sept. 11 attacks. He found himself interviewed repeatedly by FBI agents curious about a former roommate. By winter, when a couple of foreign students were attacked at his campus, he had missed school for three weeks; the Immigration and Naturalization Service revoked his student visa and deported him.

On his way out of the country, airport security forced him to strip to his underwear in front of other passengers, he said. Now he is among 170 Saudis suing the U.S. government.

"I don't say I hate the United States," he said. "I understand what happened to them and it hurt them real bad. But that doesn't mean they should treat me that way. If you're going to judge me, get to know me."

The new popular perception here of the United States was on display on a highly rated television comedy that runs every night during Ramadan. A recent episode portrayed a Saudi family that goes to the United States and stays with an American friend who used to live in the kingdom. Soon after the twin towers fall, police burst into the American's home to take away the chagrined Saudis as terrorists.

The show underscored the impact on the Saudis with the strongest ties to the United States. Even during a reception at the U.S. ambassador's residence this month, some of the guests were seething about the treatment they have received, or believe they would receive, based on horror stories they have heard.

"We could go anywhere. No one asked us where we're from," a military university professor said of his six years in the United States. Now the attitude from his former home makes him feel like a criminal. "It's humiliating," he said angrily.

An iftar dinner with several Saudi businessmen unleashed a similar torrent of grievances.

Ouday AlShaikh, the host, was flying in the United States on Sept. 11, 2001. Soon he was talking with an FBI agent who wanted to know what he was doing in the country. He and his wife spent a nervous few days secluded, waiting for a chance to come home, afraid even to go out to dinner.

Like many other Saudis, AlShaikh said he understands the need for tougher security and does not object to the FBI asking reasonable questions. But he has not returned to the United States since, even though he has an office in Washington and a house in McLean.

"Ninety-nine-point-nine percent of the Saudis that are going in are the same Saudis who have been going there for years," he said. "We can understand what everybody's going through, but we can't understand what they're doing to us."

AlShaikh, 31, and his friend, Adeeb, 33, met at American University in Washington. Now Adeeb said he avoids the capital. He thought about spending last summer at his wife's family house in Maryland, but opted for Lebanon instead.

"I just want to go somewhere and relax and forget about work, and not have to think about going to the embassy and all that," Adeeb said.

AlShaikh sighed. As he talked, he sounded more sad than angry. "You miss your friends," he said. "It's not the same."

Prince Saud Faisal: "Obstacles are being placed not in front of the terrorists . . . but in front of people who have nothing to do with that."