It's a relatively good time to be young, according to a government report released yesterday that found the nation's children doing better by many measures of health and well-being.

The most surprising finding was a significant decline in teenage smoking, which had been rising consistently since 1991. About 10 percent fewer high school seniors and sophomores acknowledged puffing cigarettes in 1998 than the year before, based on national survey results included in the annual study by the Federal Interagency Forum on Child and Family Statistics.

The national trend was likewise headed in the right direction in almost every other measure of health, education and family resources that recorded a statistically significant level of change. Juveniles were committing less crime. Teenage girls were having fewer babies. More children were going to preschool. And fewer were dying, from infancy through adolescence.

The nation's prosperity could have contributed to a few of those trends, analysts suggested. Some teenage girls, for instance, may have been careful to avoid pregnancy because they foresee attractive job opportunities. Fewer older teens have been out of school and out of work, with the kind of idle time that can lead to criminal trouble.

"Most of the indicators are going in the right direction," said Duane Alexander, a physician who directs the National Institute of Child Health and Human Development. But he cautioned that in several areas -- such as poverty, crime and teenage childbirth -- the numbers are still disturbingly high. "It still shows we have a long way to go to get children as healthy and as well off as they ought to be," he said.

The one negative trend -- out of two dozen indicators compared with previous years -- was another slight rise in the rate of underweight babies at childbirth, to 7.5 percent. "This has been a puzzle and a problem for us for years," said Alexander, though he noted that the phenomenon may be partially explained by multiple births resulting from assisted reproduction. "The more babies you have [from one pregnancy], the less they're going to weigh," he said.

A category on the nutritional quality of childrens' diets, which was included in the report for the first time, showed that most children have bad eating habits, and what's more, those habits worsen as they grow older and more independent. According to 1996 statistics, about one-fourth of children ages 2 to 5 consumed a diet that met the nutritional standards established by the Agriculture Department, while only about 6 percent of those ages 13 to 18 did. In both age groups, the rest were judged to have diets that were either poor or "needed improvement."

Most children were eating one fewer serving of fruit a day than they should, according to the report. But more worrisome was the finding that they were drinking less milk, a pattern that could result in the onset of osteoporosis in adult years.

"Milk has gotten displaced in the diet by soft drinks, by juice, by tea and other things," Alexander said. "The real solution is for milk never to be displaced as the standard drink at meals. It's the only way to get enough calcium in their diets."

While proper food remained a problem, tobacco became somewhat less of one. Among high school seniors, 22 percent reported smoking cigarettes daily in the past month when surveyed in 1998, down from 25 percent the previous year. For sophomores, the decline was from 18 percent to 16 percent. There was no change found in the 9 percent of eighth graders who smoked.

Kathleen E. Scheg, a lawyer with the anti-tobacco group Action on Smoking and Health, credited the unexpected downturn in smoking to the accumulated impact of state cigarette tax increases as well as removal of vending machines, mandatory identification checks before cigarette sales and anti-tobacco advertising campaigns.

"When the prices go up, teenagers buy less," Scheg said, referring to the tax increases. "Some states have been doing significant counter-advertising . . . I think the message is getting through to teens in language they can understand."

Although this year's school shootings in Colorado and Georgia caused a wave of national anxiety about juvenile crime, the incidence of serious violent offenses committed by teenagers continued to decline in 1997, a trend that began in 1994. The combined number of murders, rapes, robberies and aggravated assaults involving teens fell to 31 per 1,000 in 1997 from 36 per 1,000 in 1996.

Jan Chaiken, director of the Bureau of Justice Statistics, suggested that anti-gang and crime prevention efforts in major cities have paid off. Also, fewer youths from age 16 to 19 were out of both school and work -- 8 percent last year compared with 9 percent in 1997. "Partly, it's the excellent economic conditions we have," Chaiken said.

There also has been a steady and continuing decrease in teenage childbirths since 1991. In 1997, the number of girls ages 15 to 17 giving birth dropped to 32 per 1,000, down from 34 per 1,000 the previous year.

Susheela Singh, research director for the Alan Guttmacher Institute, which promotes reproductive health, said the economy could have prompted some girls to use more effective contraceptives or delay sexual activity until they are older. "They have a more clear idea of what the benefit would be of succeeding in school and preventing that pregnancy," Singh said.

Even with the decrease in children bearing children, it still happens in the United States more often than other industrial nations. The teen birth rate per 1,000 girls, Alexander said, should be in the teens.

Encouraging Trends

Indicators of the well-being of America's youth showed improvement from 1996 to 1997.

Serious violent crime

31 offenders per 1,000 youth ages 12 to 17 in 1997; rate in 1996 was 36 per 1,000.

Percentage of children ages 3 to 4 who are enrolled in preschool

48 percent in 1997; 45 percent in 1996.

Infant mortality

7.1 deaths before the first birthday per 1,000 live births in 1997; 7.3 per 1,000 in 1996.

Adolescent births

32 births per 1,000 females ages 15 to 17 in 1997; 34 per 1,000 in 1996.

Cigarette smoking

22 percent of 12th graders reported smoking in the previous 30 days in 1997; 25 percent in 1996.

One negative trend:

Low birthweight

7.5 percent of infants in 1997 weighed less than 5.5 pounds at birth, as opposed to 7.4 percent in 1996.

SOURCE: Federal Interagency Forum on Child and Family Statistics