With a million revelers and religious pilgrims expected to cram the streets of this historic city to welcome the third millennium, Italian authorities may need a little divine providence on New Year's Eve to avert a return to conditions that some only half-jokingly say may approximate those of the first millennium.

Of all the industrialized countries in Europe, Italy is by most accounts the least prepared to confront the risks brought on by the Year 2000 computer glitch.

The prospect of scattered electrical outages, telephone problems and other disruptions has even normally complacent Italian officials concerned. Outside experts worry that even small, intermittent problems with electricity and other services could snowball, and that millennial celebrants here may suddenly find themselves in an environment where Rome's splendid architecture seems its most modern feature.

"We are worried about possible Y2K-related disruptions in countries planning major tourist events--for example, Italy," warned Lawrence Gershwin, the CIA's National Intelligence Officer for Science and Technology, in October.

A recent survey by technology consultants in Britain ranked Italy's preparedness on a par with Honduras and Peru, and warned that technical maladies brought on by the computer bug will stretch well beyond Jan. 1. On that day alone, the city will be under enormous stress from huge crowds at the pope's blessing in St. Peter's Square, and along the streets where 60,000 people are slated to run in a marathon.

Italian officials insist the prospect of a catastrophic loss of essential services is low. They note that millions of dollars have been spent to reduce the risks, albeit mostly in the past few months, well behind the schedule of other large, industrial nations.

"It's been said that Rome will get through to the new millennium only with divine assistance. That's not the way it is!" Mariella Gramaglia, the vice director general of Rome, said confidently at a recent news conference.

For many Italians, an interruption in some key services will not seem extraordinary. Italians already live in one of Western Europe's most glitch-prone countries: Postal delivery is notoriously haphazard, repair work rarely seems to be finished on the first try and telephones are frequently overloaded, to mention just a few problems Rome's 3 million citizens encounter routinely. But the Italians' legendary ingenuity and experience in circumventing the obstacles created by government bureaucracy or error will doubtless give them an advantage over others in Europe.

"We don't expect any problems, other than the ones one might normally have," an official of the national telephone company noted.

Italy also will not be exposed to some of the dangers expected in Eastern European countries. It has no operating nuclear power plants, for example, and its water systems can revert to manual operation if necessary.

But some authorities are warning that Y2K--the glitch caused by the failure of computer software designers to program electronic calendars to recognize the year 2000--will cause more than the usual travails here if thousands of computers shut down or begin issuing spurious instructions. Small banks, rural hospitals and information systems run by local governments are especially at risk, according to a recent British government travel advisory.

"A situation like this has never happened before, because everything may have a malfunction" of brief duration, said Augusto Leggio, technical director of the country's Y2K commission. "Everything which is supported by an information system" could conceivably have a problem, he said, adding that he is particularly pessimistic about private companies' preparedness. "Italian people generally, by culture, don't plan."

The Italian government established its Y2K commission in January, well behind most other industrialized countries. The commission's first order of business was to draft a law mandating detailed reports on Y2K remediation, with stiff penalties for noncompliance. The law was not approved until mid-summer. By October, less than one-fifth of the relevant firms or municipalities had presented detailed plans, and even fewer had been reviewed. "It's late, but unfortunately we cannot have the time back," Leggio said.

With many computer corrections out of reach at this late date, the government has focused much of its energy on limiting the consequences of potential breakdowns. For example, an undeclared number of troops will be placed on standby to tamp down any "agitation on the part of the people" over malfunctioning phones, electrical outages, airport delays, hospital errors or inaccessible public records, Leggio said.

The government has also declared an official bank holiday on Friday, Dec. 31, and Monday, Jan. 3, essentially to allow sufficient time for repair efforts by the thousands of public employees who will be working long hours that weekend.

"We will say to the [citizens of the] city, they can enjoy themselves," Gramaglia said in a recent interview. "And we will say, it's better if you make sure you have some money . . . buy some more food, and walk up steps. I'd recommend that people don't take elevators."

Fortunately, Rome's sewage system relies mostly on gravity, not computer-driven parts, mayoral aides said. But precautions are being taken everywhere else: Electrical generators are being installed at some hospitals, where extra emergency room doctors will be on call. Key government buildings are also getting generators, and a special electrical transmission cable was installed at the Vatican.

Police officials are being trained to use satellite telephones, because their normal frequencies are likely to be swamped. One thousand new patrolmen will be deputized on Dec. 30. The country's largest supplier of electricity, ENEL, will generate a third more power than it usually does, but otherwise expresses confidence that no major outages will occur.

City officials are less sanguine. They predict that the bug may cause thousands of burglar alarms to sound at once, and also warn that mobile phones will crash, in part because of scattered electrical outages at homes and buildings supplied by a second electrical firm, city-owned Acea. Acea's equipment is so antiquated it must be reset by hand at substations, so the firm is stationing technically trained runners at key locations around the city on New Year's Eve.

Special correspondent Sarah Delaney contributed to this report.