Americans are far more socially isolated today than they were two decades ago, and a sharply growing number of people say they have no one in whom they can confide, according to a comprehensive new evaluation of the decline of social ties in the United States.

A quarter of Americans say they have no one with whom they can discuss personal troubles, more than double the number who were similarly isolated in 1985. Overall, the number of people Americans have in their closest circle of confidants has dropped from around three to about two.

The comprehensive new study paints a sobering picture of an increasingly fragmented America, where intimate social ties -- once seen as an integral part of daily life and associated with a host of psychological and civic benefits -- are shrinking or nonexistent. In bad times, far more people appear to suffer alone.

"That image of people on roofs after Katrina resonates with me, because those people did not know someone with a car," said Lynn Smith-Lovin, a Duke University sociologist who helped conduct the study. "There really is less of a safety net of close friends and confidants."

If close social relationships support people in the same way that beams hold up buildings, more and more Americans appear to be dependent on a single beam.

Compared with 1985, nearly 50 percent more people in 2004 reported that their spouse is the only person they can confide in. But if people face trouble in that relationship, or if a spouse falls sick, that means these people have no one to turn to for help, Smith-Lovin said.

"We know these close ties are what people depend on in bad times," she said. "We're not saying people are completely isolated. They may have 600 friends on Facebook.com [a popular networking Web site] and e-mail 25 people a day, but they are not discussing matters that are personally important."

The new research is based on a high-quality random survey of nearly 1,500 Americans. Telephone surveys miss people who are not home, but the General Social Survey, funded by the National Science Foundation, has a high response rate and conducts detailed face-to-face interviews, in which respondents are pressed to confirm they mean what they say.

Whereas nearly three-quarters of people in 1985 reported they had a friend in whom they could confide, only half in 2004 said they could count on such support. The number of people who said they counted a neighbor as a confidant dropped by more than half, from about 19 percent to about 8 percent.

The results, being published today in the American Sociological Review, took researchers by surprise because they had not expected to see such a steep decline in close social ties.

Smith-Lovin said increased professional responsibilities, including working two or more jobs to make ends meet, and long commutes leave many people too exhausted to seek social -- as well as family -- connections: "Maybe sitting around watching 'Desperate Housewives' . . . is what counts for family interaction."

Robert D. Putnam, a professor of public policy at Harvard and the author of "Bowling Alone," a book about increasing social isolation in the United States, said the new study supports what he has been saying for years to skeptical audiences in the academy.

"For most of the 20th century, Americans were becoming more connected with family and friends, and there was more giving of blood and money, and all of those trend lines turn sharply in the middle '60s and have gone in the other direction ever since," he said.

Americans go on 60 percent fewer picnics today and families eat dinner together 40 percent less often compared with 1965, he said. They are less likely to meet at clubs or go bowling in groups. Putnam has estimated that every 10-minute increase in commutes makes it 10 percent less likely that people will establish and maintain close social ties.

Television is a big part of the problem, he contends. Whereas 5 percent of U.S. households in 1950 owned television sets, 95 percent did a decade later.

But University of Toronto sociologist Barry Wellman questioned whether the study's focus on intimate ties means that social ties in general are fraying. He said people's overall ties are actually growing, compared with previous decades, thanks in part to the Internet. Wellman has calculated that the average person today has about 250 ties with friends and relatives.

Wellman praised the quality of the new study and said its results are surprising, but he said it does not address how core ties change in the context of other relationships.

"I don't see this as the end of the world but part of a larger puzzle," he said. "My guess is people only have so much energy, and right now they are switching around a number of networks. . . . We are getting a division of labor in relationships. Some people give emotional aid, some people give financial aid."

Putnam and Smith-Lovin said Americans may be well advised to consciously build more relationships. But they also said social institutions and social-policy makers need to pay more attention.

"The current structure of workplace regulations assumes everyone works from 9 to 5, five days a week," Putnam said. "If we gave people much more flexibility in their work life, they would use that time to spend more time with their aging mom or best friend."