It is the lack of jobs -- not laziness, criminality, a lack of motivation or other failings that is primarily responsible for drastic rises in youth unemployment in recent years, according to a study of a major experimental jobs program for youths.

The Youth Incentive Entitlement Pilot Projects (YIEPP), the largest such program ever conducted in the United States, involved 76,000 low-income teen-agers at 17 sites, including Baltimore, Boston, Detroit, New York, Dayton and rural Mississippi. It operated from early 1978 to mid-1980 at a total cost of $224.3 million.

Funded by the Labor Department under the Carter administration, the program offered a job to all low-income youths between 16 and 20 who wanted one. For the first time, it also linked school and work, requiring those who took the jobs to stay in school or, if they had dropped out, to return. Previous programs failed to link the two and in some cases, the report notes, drew youngsters away from school.

"This study suggests quite clearly that, given a choice, the kids want to work," said Judith Gueron of the Manpower Demonstration Research Corp., the nonprofit group that monitored the project. "When the jobs were available, they took them."

Among the new findings:

* Employment increased most dramatically for black youths, the group hardest hit by the lack of jobs. The employment rate for black females surpassed that for white females. (Black youth unemployment is estimated at about 50 percent, compared with about 23 percent for all young people.)

* Fifty-six percent of those eligible to work in the program took advantage of the opportunity. The plan was especially successful in attracting blacks, who joined in greater numbers and stayed longer than whites did.

* Employment in the target areas rose by 16.6 percent, an increase of two-thirds over what it would have been without the program. The impact was especially dramatic during the school months, when the employment rate under the program was nearly double that of control groups not in the program.

* While it is feasible to ask private businesses to employ disadvantaged youths, employers were much more willing to do so because of the program's 100 percent wage subsidy. When the subsidy was lowered, employer interest fell off sharply. In any case, this project relied heavily on private-sector job creation, with 55 percent of the work coming from private employers, especially "mom-and-pop" operations.

* The impact of the program on school enrollment and dropout rates was positive but less dramatic. Alternative educational programs--those leading to a Graduate Equivalency Degrees--accounted for most of the rise in return-to-school rates, suggesting that greater emphasis on this kind of schooling is needed.

To go national with the program would cost up to $1.8 billion, with the cost falling to about $600 million if only poverty areas were targeted, Gueron said. While costly, that is a bargain compared with some of the most costly (and most successful) youth jobs programs tried so far. YIEPP's cost per service year--the cost of keeping one participant in the program for a year--was $4,382, as compared with $12,041 for the Job Corps, for example.

Last December, the Reagan administration moved to end the YIEPP study before research was completed, but relented in the face of public pressure and continued the funding. Research is still under way on long-term effects of YIEPP on the ability of participants to find employment.