At least 15 percent of Americans between the ages of 16 and 19 are unlikely to become productive adults because they are "disconnected" from society as a result of drug abuse, delinquency, pregnancy, unemployment and dropping out of school, a committee of business, education and political leaders reported yesterday.

Almost 2.4 million youths -- up to half the high school population in some major cities -- fall in that group and the number is growing, according to the study by a business subcommittee of the Education Commission of the States.

The commission was set up by the states to study and advise them on the subject of education. The organization issued a widely publicized 1983 report on education and economic growth called "Action for Excellence."

Business leaders involved in the study released yesterday, in addition to expressing concern about the general social implications of the numbers, said they are worried about their future effect on the work force. Business already is suffering because of demographic changes that have reduced the available pool of young workers and will be more hard-pressed to find reliable entry-level employes, the report said.

The statistics were obtained by adding available figures on the number of adolescents who have fallen victim to each of these social problems, apparently producing for the first time an estimate of the cumulative impact, including what the report called an "unconscionably disproportionate representation" of poor, black and Hispanic teens.

"We are talking about, by conservative estimate, 1,250,000 white, 750,000 black and 375,000 Hispanic 16- to 19-year-olds at risk," the study said.

"We're about to come to a serious crunch," said Virginia Gov. Charles S. Robb (D), who headed the business advisory panel. "Virtually all of the indicators of troubled youth are going up precisely at the time the need is going to increase for entry-level workers."

Among the findings:

*Drug and alcohol abuse among young people is up 60-fold since 1960.

*Teen-age pregnancy is up 109 percent among whites and 10 percent among nonwhites since 1960; A million teens become pregnant each year.

*Teen-age homicide is up "an astounding 232 percent for whites" and 16 percent for nonwhites since 1950, while suicide is up more than 150 percent since 1950. "A teen-ager commits suicide every 90 minutes," the report said.

Authors of the report say the findings reflect larger changes in society, including dissolution of the traditional family structure and the increase in adolescent, uneducated mothers.

The higher incidence of suicide, crime, drug use and pregnancy among teens, the report said, "are all signs of alienation and disconnection. All suggest that family, community, school and other agencies of socialization and integration are not working as they once were."

And the recent educational-reform movement, it said, could be contributing to the dropout rate, which averaged 26 percent nationally in 1983 and was as high as 40 percent in many cities.

"As emphasis on individual academic achievement rises, low achievers are likely to throw in the towel," the report said. "As standards for athletic participation go up, other low achievers . . . will drop by the wayside."

Dropout rates and other factors mean that businesses, as well as the military, will be picking up more of the educational burden, according to the panel.

"Business obviously has a very special interest," said Alan K. Campbell, a business executive on the study panel and head of the Office of Personnel Management during the Carter administration. "The difficulty is for the business community to bring in and train [workers]."

Business and industry are spending $40 million a year to train employes. Increasingly, the report said, the private sector will find itself teaching remedial reading, writing and mathematics.

The study makes several recommendations and cites a number of programs that have successfully attacked the problem, including a "Cities in Schools" program operating here in Washington that links social services and business programs to the schools.

The authors call for a "profound restructuring" of schools, incorporating "far-reaching" proposals so far ignored by reformers. For example, said Mary H. Futrell, president of the National Education Association, schools could experiment with breaking up traditional scheduling that divides the school day into 45-minute periods. Leaving students with the same group for several hours a day, she said, could foster self-confidence and interpersonal skills. Other recommendations include increased early childhood education, after-school care and programs to help dropouts return to school.

Business leaders were called upon to help their employes return to or stay in school, solve transportation problems that make it difficult for young workers to get to jobs and create job opportunities that develop character and self-esteem.