JERUSALEM -- By 9 in the morning, serious young men in black skullcaps start filling the large room at the Ohr Torah yeshiva here. They come in twos or threes -- teen-agers with peach fuzz on their cheeks and side curls dangling against their ears, young adults with thin dark beards -- making their way to the hard wooden benches where they will spend the next eight hours.

By 10, the room is thick with chatter as the students, hunched over large, dusty texts, grapple with their study partners in tests of verbal agility and mental will. They argue and they cajole, flinging metaphors and insults. Occasionally they erupt in laughter.

The world of the yeshiva, a world of sages and scholars, of devotion to an ancient system of belief and to its books and rituals, survived Hitler's Holocaust to be transplanted in Israel. There it is a thriving, expanding movement in the forefront of Israel's religious revival and a key institution in the growing political clout of the black-garbed Orthodox Jews who call themselves haredim -- "those filled with awe."

Over the last two decades dozens of new yeshivas have sprung up here, either transplanted from their European origins or started from scratch. They are funded partly from abroad, but thanks to Israel's small but influential religious parties, they receive millions from the government and from related Zionist organizations, even though some are openly hostile to the modern Jewish state and many more are at best apathetic.

"We have brought back what Hitler destroyed," said Rabbi Moshe Tennenbaum, head of the Yeshiva Committee, an umbrella organization that said there are more than 500 yeshivas in Israel with a student population of at least 60,000, nearly double the number 10 years ago.

"When I came here seven years ago there were maybe 20 married men," said Rabbi Avraham Edelstein of Ohr Torah. "Now there are 90. Each gets a stipend and eats at least one meal a day here."

Yeshivas reflect varying degrees of religious orthodoxy. But most identify strongly with the haredim and the notion that Israel can be redeemed only through strict observance of the Torah, the first five books of the Bible, and related Jewish texts. As a result, yeshiva leaders and students have been on the cutting edge of the growing conflict between religious and secular Jews.

Some students serve as shock troops in stone-throwing confrontations with police over movies and restaurants open on the sabbath. Some yeshivas have refused to fly the flag on Israel's independence day, a perceived insult to most Israelis. Some aggressively recruit new students from the outside community, triggering conflicts with secular Israelis, the country's majority, who to a great extent fear and loathe their ultrareligious brethren.

One of the major sources of friction concerns Israel's citizen army. While 3,000 students in a small group of nationalistic yeshivas readily serve even while attending school, about 16,000 over age 18 receive deferments each year.

For most Israelis, army service is a key rite of passage, an almost mystical bond in an otherwise fractious and polarized nation. The deferments separate yeshiva students from the Israeli mainstream and brand them as draft dodgers and outcasts.

In a sense, that is how they want to be seen. For many yeshiva students, the secular world is a hideous jungle, a place of promiscuity and idolatry that they despise. But rather than withdrawing from that world, the yeshiva movement increasingly is setting forth to do battle with it.

"At the beginning of the state, to be haredi meant to be in a tenuous position," said Edelstein, a South African-born rabbi.

"The insularity was designed to protect us. But now there's a revolution and a new psychology. I hate to use the word, but we're definitely on the attack."

The modern yeshiva dates back to 1802 in Eastern Europe where a famed rabbi founded a school to serve Jews from all over White Russia. That world died with the Holocaust, but it was reborn in Israel in a far more favorable climate.

"In Eastern Europe the poverty was so unbearable that very few Jews could afford to even think about going to a yeshiva and it was a small struggling movement," said Menachem Friedman, sociologist and religion expert at Bar-Ilan University. "The Jewish world after the Holocaust became smaller but also richer. The modern city, with its wealth and its social welfare, has been the perfect climate for the yeshiva."

Yeshiva students come from all kinds of backgrounds, including increasing numbers of Americans, South Africans and others with different accents and experiences.

Beryl Gershenfeld, 33, was born in a Philadelphia suburb and has a master's degree in urban planning, but came to Israel on a spiritual quest. He began to find what he was looking for in a local yeshiva, became a rabbi and now operates a small school of his own for young men mostly from abroad. Among his students have been a Yale Daily News editor, a Goldman Sachs investment banker and a Wharton business school graduate.

"They come for a year or two and then return home," said Gershenfeld. "They want to live and be open in society, so I tell them they need to sink their roots deep. Your vision as a Jew has to be clear. You need to know who you are."

It is a rigorous life. Single men generally live in dormitories, rise with the sun and begin studies at 8 after morning prayers and breakfast. All day long there are classes and one-on-one sessions with fellow students. Studying continues until lights out at 11 p.m.

Married students living at home generally spend an eight-hour day at the yeshiva. They draw stipends that range from $150 to $300 a month, money that ultimately comes from the state in the form of direct payments to students or grants to the schools themselves.

Like the haredi movement, the yeshiva world gained a new dynamism after Israel's triumph in the Six-Day War in 1967 and the subsequent disaster of the 1973 Yom Kippur War. The country was plunged into a crisis of spirit and identity that was especially hard on its young.

"This is a society in constant crisis," said Israel Lippel, director of the Jerusalem Institute for Interreligious Relations and Research. "Everything is frozen, everything is tense. There is no official war yet; we're still fighting enemies. One of the natural reactions is to escape from reality towards strong belief. You leave the real world and you enter the yeshiva world."

The coming to power of the rightist Likud bloc also strengthened the movement. Searching for political allies, the Likud courted Israel's small religious parties with large-scale grants. The sum total of public funds from the religious affairs ministry and other agencies is about $120 million per year, between 25 and 40 percent of yeshiva budgets, said Jerusalem Post writer Charles Hoffman.

The Ohr Somayach yeshiva in many ways typifies the change. It began in the early 1970s as a way station for dropouts from the western counterculture and has matured into a major institution with 900 students, classes in five languages and recruitment offices in four countries.

In its sophisticated publicity campaign, Ohr Somayach portrays itself as a mainstream institution in the fight against Jewish assimilation, a place where people "learn to be a Jew." But Ohr Somayach's efforts to enter the mainstream have been frustrated by secular suspicions.

A program that brought hundreds of Israeli soldiers to Ohr Somayach was canceled by the Army two years ago because of officials' fears that the yeshiva seeks to proselytize and "steal" the soldiers. Those fears were exacerbated when nearly a half dozen pilots who had gone through years of rigorous flight training dropped out of the Air Force to enroll in yeshivas.

"It's like we're the enemy," said Weinbach, an American-born rabbi who himself has served in the Army reserve. "There's polarization and mistrust, and that tension has wreaked its political damage."

To some yeshivas, the army is another antireligious institution where men and women mix freely and Jewish teachings are scorned. Still, in time of war, the rabbis contend, many yeshivas post signs calling on their students to pray for victory. And they believe strongly their contribution is, in God's eyes, easily as important as that of the military.

"There are two types of soldiers -- those who guard the state and those who guard the Torah," said Tennenbaum, "and just like I don't force one kind of soldier to study in the yeshiva, the government shouldn't force the other kind to serve in the army."

Others disagree, but concede nothing is likely to change so long as the yeshivas are protected by patronage-laden Israeli political parties.

"It's a waste of a certain segment of our population, and Israel is too small to afford it," said Zeev Eytan, defense analyst at Tel Aviv University's Jaffee Center for Strategic Studies. "As someone who served in the army, it annoys me terribly. But this is a political reality, a part of the price we pay for our political system."