In the last decade urban Americans have markedly changed their life-styles - they are working fewer hours for pay, spending less time on family matters and devoting themselves much more to leisure.

These findings are reported in a study included in a 647-page Commerce Department book called "Social Indicators 1976," being published today.

The book is a product of four years of work by a team of statisticians headed by Denis F. Johnson, a sociologist in the department's Office of Federal Statistical Policy and Standards. The statistical office and the Census Bureau, which is also part of the Commerce Department, compiled the volume from a variety of government and private research studies.

"This is the first time that we've tried to include so much data that reflect the quality of life in the country," Johnston said.

It is the second time the government has sought to tell us how we live, procreate, spend money, commit crime, get educated, work and die. The first such effort, a 272-page volume produced by the Office of Management and Budget, came out in February, 1974, and was called "Social Indicators 1973."

The new book contains many more studies aimed at finding out how people feel about such things as their community family life, jobs and financial situations.

Johnston acknowledged that "the opinion data are the weakest because samples are small and some questions - like 'How satisfied are you with your job?' - may not elicit real feelings. But such surveys constitute one dimension of a social indicator, and they're an attempt to describe what well-being means."

The report on average hours per week spent on major types of activity was compiled last year by the Communication Research Center at Cleveland State University, and compares a sample of 1,218 urban people in 1965 with a similar sample of 726 people in 1975.

It shows that employed men married and a single spent more than 51 hours a week at work in 1965. Ten years later married men were spending 47.4 hours on the job, and single men 40 hours. Employed women spent 38.4 hours if they were married and nearly 40 hours, if they were single on the job in 1965. But in 1975 married women spent 30 hours, and single women 38.8 hours at work, the survey said.

Time spent on family care, which Johnston said includes shopping and cleaning house as well as child care, dropped from 25.4 hours a week to 20.5 hours during the decade.

Married housewives, who had devoted 50 hours a week to family care in 1965, were spending 44 hours on it in 1975, and the time married working women spent on such activity dropped from 28.8 hours to just under 25 hours.

Leisure time went up for all groups sampled, but for single men the increase was most dramatic - from 36 hours a week to nearly 45 hours.

Asked about the increase, Johnston said, know the reason. These data raise questions far more than they answer them.

"We used to think of the single male as one who's working like mad. But it looks as if he's opted for a lifestyle that includes some long skiing weekends. Economists would say that we're taking our increased affluence in the form of more leisure rather than more money.

"In households were women are working, men have an option to work less. The fact that women have more leisure time and spend less on family care could mean that children are not getting the attention they used to have, or it could reflect the vast proliferation of packaged foods and other labor-saving devices.

"Also, there's the fact that people are having fewer children. We've had 15 years of declining birth rates, and only this year has the rate started going up again."

The report includes a Gallup Poll showing that 46 per cent of thos surveyed said in 1974 that their favorite leisure activity was watching television, that 14 per cent chose reading and that 10 per cent said they preferred staying home with the family.

The figures are close to those registered in 1966, but quite different from those of 1960, when only 28 per cent preferred TV; 17 per cent staying home; 10 per cent reading and 10 per cent visiting friends.

Obviously, activities, such as spending time with the family and watching television, sometimes overlap. In other words, one might be watching television with the family. But in the poll and other surveys, the primary purpose of the activity determined how it would be listed.

For those individuals who prefer outdoor recreation, picnicking was the favorite activity, followed by driving for pleasure, swimming and sightseeing. Of spectator sports, horseracing was the most popular.

Another survey, measuring satisfation with seven major concerns of life, showed that a high percentage get a great deal of pleasure from such things as their community (49.5 per cent), hobbies and other non-work activities (57.5 per cent), family life (76.1 per cent), friendships (69.4 per cent) and their health (59.7 per cent). More than half - 52.1 per cent - said they were "very satisified" with their job; 34.3 per cent said they were "moderately satisfied," and 13.6 per cent said they were dissatisfied.

The 1976 surgey, conducted by the National Opinion Research Center at the UPniversity of Chicago, turned up strong dissatisifacion in more than 23 per cent of the respondents with their present financial situation. Another 30.7 per cent said they were "pretty well-satisified," and 46 per cent said they were "more or less satisified."

In the same study 36 per cent said their financial situation was getting better; 41 per cent said it had stayed the same, and nearly 23 per cent said it was worse.

Other attitudinal studies by the research center showed that 67.4 per cent of those polled said they were "very happy" in their marriage; 29.8 per cent were "pretty happy," and 2.7 per cent were "no too happy."

Given the growing divorce rate, the respondents were asked whether divorces should be easier or more difficult to obtain. Nearly half - 48.8 per cent - said they should be more difficult; 30 per cent said they should be easier.

Asked whether older people should live with their grown children, 53.7 per cent said it was a bad idea; 31 per cent, a good idea, and 15.2 per cent said it depends.