There was a time when a high school diploma meant that an American student had taken a giant step on the educational ladder. Now the make-or-break rung in many schools is being dropped to the ground, to the little feet of children, some of whom are facing the possibility of flunking kindergarten.

In a growing number of the nation's public school systems, kindergartners are being held accountable for specific academic and social skills: If they fall short, they can be held back.

Last spring, for example, the Minneapolis public schools held back nearly 300 kindergartners after teachers judged them unprepared for first grade. About half attended a six-week summer school, but most still were not promoted. They are spending this year in special "transition" classrooms.

The kindergarten program is the first phase of the Minneapolis schools' new benchmark testing program. Similar testing for second- and ninth-grade readiness is to begin next spring, and for fifth- and seventh-grade readiness in the spring of 1986.

The trend toward intervention as early as kindergarten is drawing fire from some parents and educators. Also, because 75 percent of the children held back in Minneapolis were minorities in a system with an overall 35 percent minority enrollment, critics are concerned that such an approach to early childhood education unfairly can stigmatize, if not penalize, the poor and underprivileged.

Okmulgee, Okla., is starting a similar readiness program for its first and second grades this year, borrowing from one in Tulsa that is in its third year. Dean Hughes, Okmulgee's head of instruction, agreed that the program there includes a disproportionate number of the small system's blacks and Native Americans.

"Okmulgee is an economically deprived area where education hasn't been a priority in many of these homes," he said. "Typically, a child from one of these homes will have no education before kindergarten. Therefore, he's handicapped from the beginning."

But, he says, "we have taken a stand. We were prepared for the worst. Our district has a long history of 'social promotions,' and we're trying to turn the tide on that." So far, he said, only five or six parents of the 80 youngsters in the program have complained.

The positive view of the early intervention programs is that they stop the downward spiral that some children begin as early as first grade. Holding back some youngsters gives them a chance to catch up before going on and allows them to gain greater confidence. The extra time allows teachers more experience with a child to determine whether problems stem from a lack of preschool training or indicate something more serious, such as learning disability.

Jacqueline Haines, a specialist with the Gesell Institute of Child Development in New Haven, Conn., says their research indicates that one-third of children in kindergarten, first and second grade are "overwhelmed" by the educational environment. The need for a transitional period is an idea the institute has promoted for 30 years, but the trend toward providing youngsters with more developmental time is new.

Haines said she understands both sides of the issue.

"Many young children need more time to develop," she said, "but in a lot of inner cities the extra time is like water over the dam . . . . These children need an enriched exposure, not just an additional year."

James T. Guines, associate superintendent of the District of Columbia school system, is emphatically opposed to the "readiness-for-first-grade" programs. Stringent standards are applied to first graders, he said, and those who do not measure up might be held back, but kindergarten is not the place to apply "someone's arbitrary standards."

It is, he added, "inhumane" and "educationally unsound."

Guines said he thinks it is better to offer a preschool program for 3- and 4-year-olds to prepare them for expected kindergarten performance than to flunk them in kindergarten, in what might be in large measure a clash of cultures.

"Little kindergartners come to school expecting to have a lot of fun," he said. "They see teachers as heroes, and they need a lot of encouragement. We take it as our responsibility to get them ready in kindergarten for the first grade. Holding them back in kindergarten would almost be penalizing them for their environmental background."

But Minneapolis School Superintendent Richard Green said he devised his system's program "using the best minds available in this school district" and wants to ensure that kindergartners "are on the right track."

"If there's a time of most flexibility of childhood or of life, it's at 5 or 6 . . . . Children know if they're not keeping up," he said. Not one parent called his office to complain about the kindergarten children being held back, he added. "If there's ever a phenomenal statistic, it's that."

But black parents were angry. And instead of complaining to Green, they turned to the Minneapolis chapter of the Urban League. Chapter President Ron Edwards, who talked with the angry parents, said they have taken a "wait-and-see" position with the understanding that the league will be their advocate monitoring the new program.

Edwards said that while parents might tend to trust the superintendent's intentions, they question whether his commitment will reach the classroom teacher. Black parents have had a running battle with the Minneapolis teaching establishment concerning teacher competence and classroom performance, he said.

Teachers have displayed "amazing confrontation and resistence" over the years, Edwards added. "The lines are being drawn."

However, the parents also realize that they "need to look to themselves," he said.

Green noted that the teacher, not the basic skills test, is the final indicator of whether a kindergarten child is held back. The test defines the child's math and language-arts skills, including color and alphabet recognition, but the teacher decides whether social skills and classroom behavior warrant promotion.

The Minneapolis kindergartners placed in the summer transition program attend a full day of school, half in regular kindergarten class and the rest in intensive academic skills instruction. They will be tested again for promotion to first grade at the end of the school year