IYADH, Oct. 18 — The textbook for one of the five religion classes required of all 10th graders in Saudi public high schools tackles the complicated issue of who good Muslims should befriend.

After examining a number of scriptures which warn of the dangers of having Christian and Jewish friends, the lesson concludes: "It is compulsory for the Muslims to be loyal to each other and to consider the infidels their enemy."

That extremist, anti-Western world view has gradually pervaded the Saudi education system with its heavy doses of mandatory religious instruction, according to Saudi officials and intellectuals. It has seeped outside the classroom through mosque sermons, television shows and the Internet, coming to dominate the public discussions on religion.

Tireless efforts to spread a fundamentalist view of Islam through Saudi-financed charities have taken the message well beyond the borders of the kingdom to places including Afghanistan.

"If you review the curriculum in Saudi Arabia, you would see that it promotes any kind of extremist views of Islam, even in the eyes of very devout Muslims," said Abdul Khadir Tash, the editor of Al Bilad newspaper.

This extremism, born of the local, puritanical Wahabi brand of Islam, constrains life here, shaping the way people live and the way Saudi Arabia greets the world. The United States seeks to build a coalition against terror with the kingdom, long a Western business and military ally, and yet the country has revealed itself as the source of the very ideology confronting America in the battle against terrorism.

These anti-Western views aid Osama bin Laden or other extremists in finding recruits, some Saudis believe, because they can mold the imperfectly formed religious creed of young, easily influenced men, convincing them that their faith condones violence against non-Muslims. Even Saudi Arabia's famous oil wealth — Saudi Aramco, the state-owned oil company, earned $80 billion last year — has been no insurance against economic and political unrest.

As a result, many fear that the pool of potential recruits is swelling as tens of thousands of young Saudis emerge with an education that leaves them unqualified for work — an estimated 50,000 per year cannot find jobs. With half the 14 million native population under age 25, some estimates say unemployment among the youngest job seekers is as high as 30 percent.

"They exploit some of the half- educated people and uneducated people and they give them the illusion that this is the real Islam," said Adnan Khalil Basha, secretary general of the International Islamic Relief Organization.

The F.B.I. list of 19 suspected hijackers in the attacks in New York and Washington includes the names of at least six missing Saudi Arabian men who left their country ostensibly to join the Islamic fighters battling the Russians in Chechnya, plus four others whose parents lost contact. They included a seminary student and recent college graduates.

Investigators are convinced that the sudden movements of the Saudis believed involved in the attack, with up to 10 young men all departing within a couple months of one other, indicate that they were likely recruited here, according to an American official.

The attacks have rekindled a debate within Saudi Arabia about the amount of religious instruction in schools. Parents say up to one third of every child's schooling is on religious topics.

In the early years the curriculum focuses on simple things like the rules for prayer. By the time Saudi students reach high school, though, they have at least one period in six devoted to study of religious topics including interpreting the holy texts and ways of keeping their faith pure.

Some parents worry that the system overemphasizes religion. A student cannot move onto the next grade if he flunks a religion class, unlike other topics. Learning is by rote, with questions discouraged

"It looks innocent, they are just trying to teach religion, but in a subtle way it is a recruiting mechanism," said a humanities professor at King Saud University in Riyadh. "If a pupil shows enthusiasm, he is recruited into their circles and then suddenly, bang! — he takes a gun and goes to Afghanistan to fight for Islam."

Those who support religious instruction contend that students need more. "Don't put the blame on the curriculum but on the misinterpretation of the Koran and the Sunnah," or the sayings and actions of prophet Muhammad, said Hamid al-Majid, a professor of education at Imam Mohammed Ibn Saud University, the country's leading seminary. "I believe the way to minimize extremism is to put greater emphasis on religious education, but in a good way."

There was a time when the mosque was the only place to learn to read and write. More secular topics were introduced, though, as Saudis educated abroad came back to run the schools. By the 1960's, a Saudi high school graduate would have been exposed to topics like Roman history and the Protestant Reformation.

In those years, however, President Gamal Abdel Nasser of Egypt preached Arab unity, fought the Muslim Brotherhood and sought to undermine King Faisal. In response, the king offered political asylum to thousands of Muslim Brotherhood members. Most ended up as teachersand junked the Saudi curriculum.

"They said this is infidel knowledge and gradually their teaching crowded out all useful information," a former government official said.

With every challenge to Saudi family rule — like the 1979 seizure of Mecca's Grand Mosque by a group of Islamic militants led by Juhaiman al-Utaibi — the dynasty ceded more ground on social affairs to shore up its own Islamic credentials.

Its princes generally viewed such matters as unimportant anyway, far inferior to glamorous ministries like defense, where government contracts generated lucrative commissions. But social affairs ministries have been dominated by descendants of Muhammad bin Abd al-Wahab, and they seek to advance his austere teachings.

Senior members of the ruling family reject the idea that they somehow allowed the education system to help shape extremists. "People can get deluded into doing acts of horrendous consequence and Saudi Arabia is not immune to having some of its citizens deluded in this way," said Prince Saud al-Faisal, the foreign minister. "We may have a different education system from other countries, but that doesn't make them more susceptible to delusion."

But other Saudis suggest the environment does exist within the kingdom because of the constant barrage of messages that Wahabi teachings are the purest form of Islam.

The attack has left the government looking for options. "Embracing the Islamist forces was a way to channel fervor and to distract criticism," one Western official said. "Now it is the Islamists who are a threat. It has become problem No. 1."

Saudis and Western diplomats said the Saudi government seemed to have inadvertently exported that attitude through large investments in spreading the faith. The kingdom has built hundreds of mosques worldwide, but many propagate the anti- Western, Wahabi attitudes because their prayer leaders were trained on scholarships at religious institutions here or in Saudi-financed schools.

Inside Saudi Arabia, at least through the 1970's, mosques were strictly for prayer, with one sermon each Friday. Now speeches unroll almost nightly in some of them, long after prayers end.

Nor is the anti-Western extremism limited to mosques. Sheik Yusuf al- Qaradawi, a religious sheik with a popular Al Jazeera television show, often adopts an anti-Western stance.

Recently he entertained a question from a viewer named Ali in Saudi Arabia asking whether American civilians working in Islamic lands should be considered warriors and warned to leave or be killed. The sheik did not flinch at the idea, giving a legalistic answer that all those invited in deserved protection. A guest columnist in Al Watan, Saudi Arabia's answer to U.S.A. Today, wrote that Islam and the West are natural enemies, disputing a writer who said the religion was peaceful.

"He says that Islam means peace, while I say no interpretation ever said so, and God said to fight all the infidel," wrote Mohammed al-Rameh of the Supreme Institution for the Judiciary. The dissenting response came from someone in Spain, not Saudi Arabia.

The arguments also roll forth on the Internet. Hamoud al-Shuaibi, an elderly sheik who issued a fatwa, or religious ruling, condemning the American attacks on Afghanistan, answered a question on the Net about when jihad, or holy war, is permissible. "Jihad is allowed against infidels like the Jews, Christians and atheists," he answered in part.

The extremely religious people focus much of their attention on social matters, handing out colorful pamphlets with bold type at shopping malls. One pamphlet said it was a sin even to vacation in the West, and another condemned those who wish non-Muslims well on their holidays.

The very same lessons were echoed in the nearly 20 pages in the high school textbook devoted to the involved principle known as "Al Wala and Al Bara," or showing loyalty to Muslims and shunning outsiders.

"One of the major requirements in hating the infidels and being hostile to them is ignoring their rituals and their festivities," the textbook says.

Later in the chapter it is recommended that Saudi youth do nothing to imitate non-Muslims in the way they dress, walk, eat, drink, or talk.

"It is social fanaticism," said Jamal Khashoggi, the deputy editor in chief of The Arab News, "but it takes just a few small adjustments to turn it into political fanaticism."