Imitating its namesake in the Appenine Mountains of southern Italy, this village of 1,500 clings to a forested ridge in the Poconos.

Not many outsiders wind their way up here, and those who do may first think they have stumbled upon a ghost town. During the day, the children all are in school while nearly every adult is away at work in nearby towns. Vegetable plots and grape arbors adjoining modest frame houses await the return of their gardeners. On front porches, which often are built right up to the sidewalks, chairs are lined up ready for the evening's passeggiata.

That Old World custom reanimates Roseto's streets in a leisurely promenade punctuated with frequent stops to share news of the day and gossip about the great strings of extended Italian-American families who live here.

"You go down the street, and everybody says, `Hello, hello'," said Anita Renna, 43. "You feel like you're the mayor."

As background music for that procession, the evening bell rings at Our Lady of Mt. Carmel Roman Catholic Church, its echoes wafting throughout the village. After dinner, a firefighter goes to the second floor of the municipal building to open the social club whose bar proceeds support the volunteer company. Its two trucks, one of them a classic, early-1960s model, are housed below.

At first blush, Roseto seems a diorama of what once was the nation's ideal lifestyle--neighbors who looked after one another, civic-minded joiners and doers who formed the grass roots of American-style democracy. It seems to showcase those virtues that have all but disappeared elsewhere in what has become a Nation of Strangers.

But stay a while and the picture takes a sharper focus. Long-time residents complain of the strangers--"New Jersey people" they call them-- who recently have begun to move into the once monolithic community tracing back almost entirely to old-country immigrants. They point to clues of changing lifestyles outsiders would miss-- fenced-in yards, satellite dishes, expensive cars.

In generations past, there was virtually no play in Roseto's tight-knit fabric of community. Mamie Ciliberti, 73, recalled: "When I was young, this was our little world up here. We didn't associate with anyone different from us until we went to high school in the town at the bottom of the hill."

Indeed, at one time the village came to be a living laboratory demonstrating that neighborliness is good not just for the body politic but for the human body as well.

Thirty years ago, the researchers who came to that conclusion were led here by a bewildering statistic: In defiance of medical logic, Rosetans seemed nearly immune to one of the most common causes of death. They died of heart attacks at a rate only half that of the rest of America. Doctors at first were mystified, in that residents led what medical textbooks predicted would be short lives.

Beginning with the first arrivals from Roseto ValFotore, the men of the village smoked and drank wine freely. They spent their days in back-breaking, hazardous labor, working 200 feet down in nearby slate quarries. An additional health peril awaited them at home each evening: groaning tables of traditional Italian food, modified for local ingredients in ways that would drive a dietitian to despair.

The Mediterranean diet, with its use of olive oil rather than animal fat, has been touted lately for health benefits. But poor immigrants couldn't afford to import cooking oil from their homeland and instead fried their sausages and browned their meatballs in lard. Yet, inside the resulting hefty bodies beat unusually healthy hearts, a combination that just didn't compute.

The paradoxical longevity now known in medical literature as the "Roseto Effect" might never have been documented except for a chance conversation over a couple of beers in 1961. Dr. Stewart Wolf, then professor and head of medicine at the University of Oklahoma School of Medicine, had bought a farm in the Poconos as a summer retreat and got to chatting with a local physician. The local doctor happened to mention that heart disease seemed far less prevalent in Roseto than in adjoining Bangor, where non-Italians were predominant.

Skeptical but intrigued, Wolf checked death certificates for Roseto and surrounding towns for the previous seven years. He found that the men of Bangor had an annual average of heart attack deaths that closely paralleled the national average.

When Wolf and his sociologist co-author, John G. Bruhn, published their findings in the Journal of the American Medical Association in 1966, Roseto's cardiac mortality rate traced a unique graph. Nationally, that rate rises with age. But for Roseto it dropped to near zero for men 55 to 64, an age group elsewhere at high risk. For men over 65, the local death rate was 10 per 1,000, half the national average, and-- uniquely-- there were more widowers in town than widows.

The investigation of the Roseto Effect went far beyond gathering death certificates. Over a four-year period, two-thirds of the village's adults were persuaded to climb the stairs to the Council Chambers, where temporary examining rooms had been curtained off. There, they were poked, prodded and extensively interviewed. A team of 11 dietitians grocery shopped with the Rosetans, went home with them to watch what they ate--and, of course, were invited to share the meals. Similar exams were made on about a third of the populations of two nearby towns.

Instead of solving the puzzle, all that data simply ruled out any genetic or other physical sources of the Rosetans' resistance to heart disease.

When, however, the doctors looked beyond the Rosetans to Roseto, two statistics jumped out as potential clues: Both the crime rate and the applications for public assistance were zero. The researchers looked again at their surveys of family life.

"We were struck by the fact that all the houses contained three generations of the family," said Wolf, now a professor of medicine at Temple University. "Rosetans took care of their own. Instead of putting the elderly on the shelf, they were elevated, so to speak, to the Supreme Court."

Step by step, the scientists were led to conclude that the Roseto Effect was caused by something that could not be seen through a microscope, something beyond the usual focus of medical researchers.

It seemed that those groaning dinner tables offered nourishment for the human spirit as well as the body. In fact, all the communal rituals--the evening stroll, the many social clubs, the church festivals that were occasions for the whole community to celebrate--contributed to the villagers' good health.

In "The Power of Clan," an updated report on their studies expanding the time frame to the 50 years between 1935 and 1984, Wolf and Bruhn observe: