Prime Minister Ehud Barak's governing coalition was thrown suddenly into turmoil tonight--not by enemies abroad or terrorists at home but by a gigantic electrical turbine as wide as a house and half as long as a football field.

The crisis was triggered when the government defied the country's largest religious party by deciding to transport the 300-ton piece of equipment to a power plant during the Sabbath, which started at 8 this evening.

The move had been fiercely opposed by the ultra-Orthodox Shas party, which adheres strictly to Jewish law prohibiting driving and other forms of labor during the Sabbath. Shas threatened to quit Barak's coalition if the government heeded the police recommendation to transport the turbine on the holy day, when roads are relatively empty.

Shas, led by rabbis and backed by working-class Jews of North African origin, is the second largest party in Barak's 75-member coalition in the Knesset, the Israeli parliament. If its 17 legislators quit the government, Barak would lose his majority in the 120-seat parliament and face his first real crisis in office.

The dispute over the turbine--55 yards long and 10 yards wide--is the latest and largest symbol of the bitter culture war between ultra-religious and secular Jews. The strains and, often, outright hatred between the groups were a defining element of the elections in May that brought Barak to power.

Barak had hoped to avoid a bitter coalition battle barely a month after taking office. He insisted the dispute over when to move the turbine was not political, but few Israelis seemed to share this view--particularly not Shas members.

"If the government were to decide to move it on the Sabbath, then I don't believe anyone who wears a skullcap would be able to continue sitting around the cabinet table," said Shas's Eli Suissa, minister of national infrastructure, referring to the ultra-Orthodox members of Barak's government.

Faced with Shas's opposition, the government seemed to back down despite police warnings that moving the turbine during the week would paralyze Israel's densely populated coastal strip, impede access to hospitals and jeopardize public safety.

But in a surprise move perhaps meant to minimize physical interference from ultra-Orthodox protesters, the gigantic turbine, secured to a flatbed truck, began to roll about an hour after Sabbath began at sundown. Since religious Jews do not use the telephone or listen to radio or television once the Sabbath begins, few knew that the turbine was rolling.

But roll it did. Starting just north of Tel Aviv, the turbine lumbered south at barely 5 mph along Israel's main coastal highway, escorted by about 50 police cars. The 50-mile journey to a large power plant in the port city of Ashkelon was expected to take about 16 hours.

As the truck rumbled through B'nai Brak, an ultra-Orthodox suburb of Tel Aviv, about 20 religious Jews shook their fists at it. But as the load passed Tel Aviv's other nonreligious neighborhoods, more than 100 secular Jews lined the route and applauded.

The chasm between ultra-religious and secular Jews dominated not only Israel's elections but also Barak's efforts to form a governing coalition this spring. Many of Barak's overwhelmingly secular supporters opposed his decision to include Shas in his coalition, fearing the party would seek to force its agenda on secular Israelis. But by allying himself with the relatively dovish Shas--and awarding it control of four ministries--Barak ensured the party's support for his top priority: reviving stalled peace talks with Israel's Arab neighbors.