The young Israeli artist, his eyes occasionally straying nervously to nearby tables for possible listeners, sat in a small Jerusalem restaurant and talked in a low voice about his personal war with Orthodox Judaism.

With a group calling itself Tanach -- a Hebrew acronym for Terror Against Ultra-Orthodoxy -- the youth had just completed a dangerous, late-night mission of vandalism in Jerusalem's most fervently religious neighborhood, the Mea Shearim quarter.

Disguised in the traditional long black coats of Hasidic Jews, the young secular Israelis covered the facades of synagogues and religious schools with drawings of nude women and pigs and obscene slogans in Hebrew and English.

The youth, who spoke on the condition that he not be identified, said his precaution was based not on fear of arrest for vandalism, but on the likelihood of vengeance attacks by the outraged Orthodox Jews. He said it was the most daring secular vigilante raid yet in a dangerous Orthodox neighborhood in an increasingly bitter cycle of violence between religious and secular Jews in Israel.

"They said it: 'God help them if we find them.' But this is only the first salvo of a battle to prevent a complete takeover of Jerusalem by these fanatics. They're surrounding the city, and either we stop them or there will be civil war," said the militantly secular Israeli.

The graffiti spree in Mea Shearim, a reprisal for a series of arson attacks by Orthodox Jews on public bus stop shelters -- because they carry advertising posters that the Orthodox consider provocative -- was the latest round in the conflict. In the last several months, other secular vigilantes have ambushed Orthodox Jews as they prepared to burn offensive bus stop shelters and held them for the police.

The recent incidents have dramatically underscored the steadily growing polarization between the increasingly militant religious right and the two-thirds of Israel's population that regards itself as representing the secular Zionist movement that founded the Jewish state 38 years ago.

This polarization, according to some widely respected analysts of political and social trends, potentially poses at least as great a threat to Israel's stability as that posed by outside Arabs.

"The radical fringe groups on both sides are growing every day and are becoming far more militant and aggressive. Neither side cares to be tolerant, and it is deeply disturbing," said Daniel Tropper, founder and director of Gesher, a voluntary organization that is trying to bring the two camps together in seminars and courses in Judaism in hopes of achieving a detente.

An Orthodox Jew in the Mea Shearim quarter, a warren of narrow streets reminiscent of the 19th-century Hasidic ghettos of Eastern Europe, with a large sign at its entrance warning women they face danger if they fail to respect the residents' norms of modesty, characterized the recent clashes as a "Jewish jihad," or holy war, and said that he kept a gun in his home to protect his family from "Godless thugs."

The current secular backlash against perceived excesses by the 30 percent of Jerusalem's population that represents the Haredim, or ultra-Orthodox Jews, follows several years of steadily mounting militancy by the zealously religious Israelis in their campaign to tighten the halacha, or ancient Judaic law, and apply it to everyday life throughout Israel.

The fundamentalists routinely stone automobiles passing near religious neighborhoods on the Sabbath and frequently attack and injure secular women who enter those neighborhoods with their arms uncovered or who are otherwise "immodestly" dressed.

They ransacked an Israeli census office on the grounds that counting people violates divine law, and they have strung piano wire across darkened streets in their domains to discourage Sabbath motorists -- a practice that caused the decapitation of one jeep driver in Tel Aviv's Orthodox Bnei Brak neighborhood.

They have violently demonstrated against mixed-sex swimming in municipal pools, attempted to forcibly close movie theaters and soccer stadiums that open on the Sabbath, and confronted police in violent protests against autopsies in public hospitals and against archeological excavations near ancient Jewish burial grounds.

With each of their successes, the ultra-Orthodox Jews appear to become bolder, fueling what Jerusalem secular leader Uri Huppert called "religious xenophobia and a Khomeini-like Jewish fundamentalism."

A young Israeli secretary, reflecting on the increasing stridency of Orthodox Jews that she found here when she immigrated from the United States, said, "I didn't come here to be intimidated by a bunch of Jewish mullahs."

Huppert, a lawyer and chairman of the New Coalition Against Religious Coercion in Israel, warned that the rightward trend in religious expression not only poses internal dangers for Israel but, if translated into anti-Moslem sentiment, could add to regional instability and a major source of strategic concern to the West.

Noting the uncovering of conspiracies by religious zealots in recent years to blow up mosques, Huppert said that "one more attempt like that could lead not only to fundamentalist totalitarianism, but to an international explosion."

The seeds of religious polarization in Israel can be traced to the beginning of the Zionist movement in 19th-century Europe, when secular Jews seeking to resettle a Jewish homeland in Palestine quarreled bitterly with dynastic rabbis of the Orthodox Hasidic movement, who maintained that the creation of a state of Israel before the coming of the Messiah would be a blasphemy.

While the more moderate branches of the Orthodoxy eventually began to reinterpret their views on Israel, concluding that the new state would be an opening for the Messiah to effect the final redemption, some groups today still openly oppose the state. A few of them burn Israeli flags on Independence Day, and one of the fringe sects, Neturi Karta, encourages the Palestine Liberation Organization to defeat Israel.

Because virtually all of Israel's governments since the country's founding have been dependent on religious parties to form coalitions for a parliamentary majority, the dominant Labor and Likud parties traditionally have had to keep on good terms with the Orthodox, which, according to some secular leaders, has encouraged religious extremism.

However, in Huppert's view, the "Trojan horse of secular Zionism" was the relatively moderate National Religious Party, which for 35 years dominated Israel's religious parties until its influence was diluted by the rise of smaller Orthodox parties in the last two elections.

It was the National Religious Party, Huppert noted, that divided the country's educational system into religious and secular departments; created a twin rabbinical system for Ashkenazim, or Jews of northern and eastern European origin, and Sephardim, or Jews from North Africa, Spain and the Arab world; strengthened rabbinical law through legislation, and forced through measures that undermined the Reform and Conservative movements in Israel.

"The NRP created the climate for theocratic rule through democratic means, and then itself was destroyed by the ultra-Orthodox parties," Huppert said, noting that it dropped from 12 seats to four in Parliament in two elections, while the Orthodox parties gained eight seats and a commanding position in a coalition system in which a handful of votes can wield considerable influence in forming a government.

"Now the Orthodox say they have to dictate how Israel is to be managed, because the Messiah will be angry if the divine rules are not followed. If we continue to buy Orthodox fundamentalist influence, we are establishing the same trend that was established by the mullahs in Iran," said Huppert.

Moreover, he said, such extremism inevitably expresses itself in anti-Moslem campaigns, such as a recent effort by messianic Jews to return to the Moslem-controlled Temple Mount in Jerusalem's Old City and reestablish a Jewish temple there. Since a few days after the 1967 War, when Israel captured East Jerusalem, Jews have been barred from praying on the Temple Mount, which is also sacred to Moslems. The anti-Moslem movement, Huppert said, will only exacerbate the Arab-Israeli conflict and weaken Israel's security.

However, the leader of the Temple Mount campaign, Gershon Solomon, contended that a transfer of the Temple Mount from Arabs to Jews would unify Orthodox and secular Jews more than anything else.

Warning that secular-Orthodox polarization is "maybe the most dangerous problem in Israel today," Solomon, who heads a militantly messianic group called the Temple Mount Faithful, said, "In order to exist here, we must build on our Jewish identity. The way to do that is reoccupy the Temple Mount, which for thousands of years has been a symbol of unifying Jews. It will strengthen the ties between secular and religious Jews, and the conflict will end."

However, Solomon, a devout Jew who is not associated with Orthodox groups, said the ultra-Orthodox would have to moderate their positions, and that militant seculars would have to become more tolerant of religious Jews in order to achieve a meeting of the two groups.

Tropper blamed the recent escalation in secular-Orthodox violence on a lack of forceful leadership in both camps, which, he said, leads to radical fringe groups on both sides dominating the debate.

Tropper, who has been organizing seminars at a retreat in Safed, in the Galilee, said, "The minute you show a religious Jew that there are decent, serious seculars who are interested in more than just picking up girls in Tel Aviv, and you show a secular that there are thoughtful, moderate religious Jews, you have made progress."

However, the young Israeli artist who painted nude women and pigs in religious neighborhoods appeared unconvinced that moderate Orthodox Jews will prevail over the Haredim.

Vowing to return to Mea Shearim on an anti-Orthodox vigilante raid, he said, "A few years ago we wouldn't have thought of doing this. But these black coats have changed the status of religion into a political thing, just like the popes in the 14th century changed religion into a political force."