The contrast is a happy one--last spring, hundreds of parents crowded into the high school cafeteria to hear the final plan for desegregating the city's schools; very few people looked pleased, and most were grumbling.

Last week, hundreds of mothers and fathers--this time with hundreds of children--crowded onto the playground of the Tobin School. Nobody was frowning; they were too busy eating hot dogs, singing or getting to know each other.

Two weeks after the opening of school, the first stage of desegregation in the elementary system seems to be going well. "Schools opened without incident," school publicist Burt Giroux announced after the first day. "It's all gone absolutely smoothly," he added yesterday.

Enrollment figures indicate the success of the program--which the city adopted voluntarily, keeping in mind possible state action to correct racial imbalances. Despite predictions that some parents would pull their children out of the system rather than have them bused, the first statistics show steady enrollment.

Preliminary figures on the Cambridge school population indicate more than 6000 students are attending classes this fall--almost 500 students more than the state had predicted.

About 800 students had to switch schools because of the new plan. Of those, about 175 requested exemptions.

Only 69 of the transfer requests were granted, Giroux said, adding that some families appealed the decisions.

Two years of careful planning precipitated the smooth beginning, Giroux said. An endless round of meetings and reports prepared last winter and spring are proof of community involvement in the plan, he added.

"Parents and teachers have had so much to do with the plan that they have a stake in making it work," he added.

He also credited the peaceful opening to Cambridge politicians, who worked hard to avoid court intervention in the school system by adopting the voluntary plan and by not exploiting desegregation for their own ends.

The third reason for success--which school officials play down in public--is that the desegregation plan adopted this year is only a halting first step. Potentially more explosive stages are yet to come.

Gerrymandering

The School Committee redrew district boundaries enough to balance the schools for only one year; now they must figure out how to keep shifts in population from upsetting the statistics annually.

The only workable proposal so far is a system of zones. That plan would send youngsters new to the system to any of several schools, regardless of their distance from the children's homes. Such a system--which would affect more children--could draw heavy fire.

One Small Step

State pressure prevents the School Committee from delaying for long. When the preliminary measures were announced in the spring, state Board of Education officials called it "only a first step."

So Cambridge officials will have trouble keeping the momentum going. But for now, most everyone is smiling.