Jim McEuen was home sick the day his father died. He could have reached the hospital in a few minutes, but he first had to drive downtown to get his wife at work, then back to a Bethesda day-care center to pick up their son.

By the time he arrived at Holy Cross Hospital in Silver Spring, his father was in surgery.

"Shortly after I got there, they told me he was dead," McEuen said. "It was that delay that prevented me from saying goodbye to him."

McEuen tells this story often, matter-of-factly and without rancor, when he is asked about the simultaneous and often competing pressures he has faced as the son of elderly parents and the father of young children. The conflicting demands of that day, he said, epitomize what he calls "the new family dynamic."

McEuen, like many of his Baby Boom peers, is facing the new reality of dual responsibility -- struggling to meet the needs of aging parents who have, in some cases unexpectedly, become less self-sufficient just as his family gears up to meet the demands of young sons.

Unlike families in the past, in which children were often into adulthood by the time their grandparents needed help, today's Baby Boomers are ever more likely to find themselves caring for both generations at once.

The growth of the so-called "sandwich generation" is the coincidental result of two demographic trends: prolonged life span, largely due to advances in medical technology, and the tendency among couples to delay marriage and childbirth into their thirties.

In the past, couples typically began having children in their twenties, and so when their parents became frail, at the age of 70, for example, the youngest generation was already into its twenties and less likely to be dependent.

But at the same time that social and economic changes have led couples to delay childbirth, life expectancy has increased. Men and women today will spend about twice as many adult years with a surviving parent than they would have in 1900.

Thus, despite the lingering expectation that generational dependencies should unfold in well-timed sequence, American home life is increasingly an experience that one sociologist calls "interwoven biographies." While this can mean a graceful blending of young and old, the reality is often one of daily pressure in managing logistics, overwhelming responsibility and guilt over unmet expectations.

Families already frustrated in their search for the right day care for their toddlers may find themselves looking at the same time for a good "elder care" program for their parents. Weekend time must be parceled out between trips to the mall for school clothes and grocery shopping for grandparents.

There are medical bills for three generations. And the trauma of watching parents decline may only be heightened by the stress of dividing precious time among family members.

"The constant feeling is one of being stretched thin," McEuen said.

Jim and Caroline McEuen, both 42, waited until they were in their thirties to have their two sons, 9-year-old Jonathan and 3-year-old Ian. Jim McEuen's mother, Estelle, 72, is debilitated by a central nervous system disorder.

The demands of this demographic puzzle hit McEuen abruptly upon the death of his father three years ago. His mother needed full-time care immediately, his parents' home needed to be renovated and sold and, on the day of his father's funeral, the McEuens discovered they were going to have their second child.

Two weeks later, Estelle McEuen entered a nursing home in Olney. Two months later, Caroline McEuen's mother died of cancer. Later that year, Ian was born.

It was a period of turmoil and change that "we still haven't gotten over," McEuen said.

Today, family life has fallen into a more settled pattern, but one still fraught with the realities of constant duty.

McEuen, an editor at the International Monetary Fund, must take time from work to take his mother to the doctor. He prepares her taxes, shops for her and visits her on Sundays. It is a long drive, and by the time he gets home, it is often dark.

Jonathan regularly asks why his father must go, insisting instead that he stay home and play, or take him to a birthday party or Cub Scouts.

"He's a very understanding kid. He doesn't hold grudges," McEuen said. But he makes straightforward judgments, "and his judgment is that my mother makes too many demands."

"That's the cost of being in the 'sandwich.' You try to balance, but sometimes you can't. . . . Where do the loyalties lie? They have to lie with the future and not with the past. It's not triage; we've been able to do both."

But then he laughs: "Look at the metaphor. 'Sandwich generation.' What's in the middle? Chopped meat."

Sociologists agree that the number of families with such dual responsibilities is greater than ever before, but estimates vary widely.

The Agency for Health Care Policy and Research, an arm of the Public Health Service, estimated last year that there are 3.6 million men and women with children under 15 who also take care of a disabled parent. That number represents 7.4 percent of parents with children in that age group.

The study counted only those people whose parents needed help with basic, daily activities, such as eating or dressing, and did not include families who provide less critical assistance, such as taking their parents shopping, or visiting regularly.

The Older Women's League estimates that nearly a third of women will give care to both elderly parents and children, and argues that women can expect to spend 18 years of their lives helping an aging parent and 17 years caring for children.

"The dependency burden has increased," said Jane A. Menken, a sociologist and demographer at the University of Pennsylvania, in a 1987 paper written with two colleagues. "Not only has time spent with old and young dependents increased, but so has the number of years with simultaneous obligations to both groups."

Another set of trends -- the entry of women into the labor force and more single-parent families -- have complicated the pressures, meaning there are fewer caretakers at home. Taken together, the demographics paint a chaotic family portrait.

Diane Krevolin lives in West Haven, Conn., with her husband, three children ranging in age from 11 to 5, and her 80-year-old mother, Evelyn Skornik, who suffers from what her daughter describes as dementia.

The household scene on weekday mornings is frenetic: Krevolin is up before 6 a.m., then wakes her mother, who must get ready for an adult day-care program.

Krevolin gets herself ready for her job as a supervisor in the state unemployment office, at the same time checking in often -- as many as a dozen times a morning -- to push her mother along. She wakes up the three children by 7 a.m., helps them get dressed and fed, makes their lunches, signs notes for school and is out the door by 7:45 a.m.

Her mother is picked up by a bus at about 8:20. And her husband, Daniel, a city planner in an anti-poverty agency, drops the children at their bus stop at 8:25.

After work, Diane Krevolin usually takes a child or her mother to an appointment, gets home by 5 p.m., makes dinner, helps with homework, gives baths and puts the children to bed.

"Then I do the dinner dishes and collapse, hopefully, by 11," she said.

Krevolin said the crush of family and work is complicated by her mother's disability -- she barely communicates and is unable to care for herself. But Krevolin promised her father at his death that she would not put her mother in a nursing home.

"You have to do a lot of planning to pull it off," said Krevolin, who is 42. "It doesn't leave any time for spontaneity. It affects career decisions. My husband was out of work, and it meant we couldn't up and move" to follow his career, she said. "Sometimes, it's overwhelming."

Barbara Kane is co-founder of Aging Network Services in Bethesda, which helps families in which parents and children do not live near one another find appropriate care for elderly parents. She said those in the middle "feel like they have to be all things to both generations." But the solutions, including the option of having a parent move in, often are difficult.

Kane said families are grappling not only with the logistics of managing three generations but with the guilt of divided loyalties. "Sometimes my clients feel if they didn't have children, they could be more available" to their parents, "or if they didn't have elder care, they could be more available for the children."