An M-16 rifle slung over his shoulder and a floppy green hat planted on his head, Zvi Schlissel squinted across the sun-scorched no man's land between Israel and Jordan.

"If not me, some other Jew would be here," said the Brooklyn-born Israeli, explaining why he decided to join the army and defy the norms of his community of ultra-Orthodox Jews. "At least I feel bad about it."

A glib, good-natured 19-year-old, Schlissel used to spend all day in seminary studying the Torah. In January, he left the yeshiva and volunteered for an experiment--a brand-new army platoon that seeks to combine combat training with the rigors of devout faith.

It is an experiment without precedent in Israel, and one full of artful compromises: Female soldiers are barred from the platoon's base near the Dead Sea and so are secular publications and non-kosher food. To finesse the ban on writing on the Sabbath, soldiers in Schlissel's platoon use pens filled with disappearing ink to keep logs on patrol each Saturday.

Still, the army demands that no corners be cut: Schlissel and his comrades underwent four months of basic training capped, by a 25-mile march in midsummer heat. They make their usual rounds on patrol even on the Sabbath, when devout Jews are ordinarily banned from carrying arms, riding in cars or using two-way radios.

"We look for the middle road wherever it can be found," said Lt. Col. Eitan Ozeri, deputy commander of Schlissel's brigade. "It's a marriage of practicality and faith."

Conceived as a model for future accommodation between Israel's ultra-Orthodox and secular worlds, the army's all-religious unit remains a tiny, volunteer aberration. But it reflects the search for a middle road, a convivial compromise in the widening, surly divide between religious and secular Jews.

Since Israel was formed in 1948, it has allowed the ultra-Orthodox to study in seminaries instead of serving in the army, a requirement for virtually all other Jews. That deal, struck by Israeli founder David Ben-Gurion, ruffled no feathers when it took effect at mid-century; at the time, it applied to just 400 ultra-Orthodox Jews, a tiny minority generally thought to be facing extinction. But ultra-Orthodox Jews have thrived in Israel, and today about 30,000 are exempt from the draft--an inequity with no basis in law.

The blanket religious exemption infuriates many secular Israelis, who believe it tears at the fabric of national unity. They wonder why they should be required to serve their country--and, by job description, risk dying for it--while thousands are allowed off the hook.

Last December, Israel's Supreme Court ruled the exemption illegal and ordered parliament to legislate a solution within a year. Ehud Barak, the new prime minister, promised in his election campaign to compel at least several hundred ultra-Orthodox teenagers to submit to the draft each year.

But in the hard-nosed politics of Israel's religious-secular battle, Barak's promises were soon eroded. The religious parties Barak needed for his broad-based coalition insisted that no Jewish seminary student be compelled to serve in the army if he prefers to study the Torah.

The matter was referred to a special commission. But as things stand now, Barak's stated goal of lifting the blanket exemption enjoyed by ultra-Orthodox Jews seems elusive. In a deal he worked out with the religious parties, Jewish seminary students are to be allowed to stick to their studies to age 24, then enter the job market without an obligatory full stint in the army.

That represents a revolution for ultra-Orthodox men. Previously, they had two options: Either they could stay in a yeshiva until they could obtain a permanent draft exemption--at age 35 at the earliest--or they could drop out and try to find illegal work. Since employers are bound by law only to hire veterans of the secular, co-ed army, it is impossible for most young ultra-Orthodox men to find legal work.

Religious politicians relished their victory. "In the army you eat, dress and hear things that you wouldn't in the yeshiva," said Meir Porush, leader of the United Torah Judaism party. "We are very observant, and as conservatives we notice these things."

In his first weeks in office, Barak has focused his attention almost exclusively on diplomacy, determined to reinvigorate Israel's stalled negotiations with its Arab neighbors. Some Israelis worry that the new premier is so intent on preparing the ground for peace in the region that he will neglect to secure peace at home, particularly between the country's ultra-Orthodox and secular camps.

The competition between the two is a bad-tempered standoff that in the past few weeks has only toughened. In a rapid succession of incidents, ultra-Orthodox and secular Jews have spit, shoved and screamed at each other in fights over the streets they drive on, the business hours they keep, the clothes they wear.

In one episode, police scuffled with a mob of ultra-Orthodox Jews as they tried to close a street in Jerusalem that is open to secular traffic on the Sabbath. In another incident, secular shops open on the Sabbath were fined by inspectors from a religiously controlled government ministry. In recent days, secular women who work for the Education Ministry have been harassed and spat at by religious Jews for wearing short-sleeved summer clothing deemed insufficiently modest.

The danger in all this, say some analysts, is that it could distract Barak from his principal goal of securing a broad peace deal with the Palestinians, Syrians and Lebanese.

"Ultimately, the success of this task depends on the measure of self-restraint that secular and religious leaders will be able to display," said Emanuele Ottolenghi, professor of Israeli politics at Oxford University.

If there is any hopeful sign on the horizon, it may be the army's religious unit, which, though small, is expected to triple in size this year.

Before the 30 soldiers in the platoon enlisted, many or most were misfits in their ultra-Orthodox communities, often attracted by the secular world even as they studied the Torah for hours each day.

To deal with that, and to win religious backing for the new unit, the army allows several rabbis to visit the remote base each day. In basic training, instruction in weapons, tactics and fitness is supplemented with daily prayers and religious instruction to keep the soldiers focused on the Torah.

"Soldiers who weren't strictly religious before joining the army sometimes become more religious in this unit," said Ozeri.

Visits by most outsiders are banned, and special rules apply. Soldiers can be punished for having secular newspapers. In the unit's briefing room, signs on the wall admonish the troops to toe the religious line:

"You are not allowed to smoke on the Sabbath--by order!" says one. Another reads: "You must keep kosher--by order!"

In addition to religious instruction, all the soldiers must take basic courses in science, math, Hebrew and history, subjects barely covered in the seminaries. Most of the troops are ignorant of nonreligious subjects, their teachers say. In a biology class, a number of soldiers said they believe human beings have two hearts. In math, most troops were at a sixth- or seventh-grade level.

Schlissel said he was motivated to join the platoon so that he could enter the job market sooner and support his family when he has one. He said he is proud to serve in the army and believes he contributes to Israel's security by patrolling the Jordanian border.

Still, he said, the trade-offs are tough. "It's one of the hardest things I can do, to get into a Jeep and drive [on the Sabbath]. But somebody has to do it, or we might as well put up a sign for the Jordanians saying, 'Hey, it's Saturday, please come on in.' "