Supporters of the Humphrey-Hawkins "full employment" bill defended the measure yesterday against charges that it is toothless and unrealistic, and asserted it would prove "a significant and meaningful stop forward" "award" toward overcoming joblessness.

At a press conference called to announce their endorsement of the measure, spokesmen for the Full Employment Action Council, a coaltion of 32 civic groups supporting the controversial legislation, disputed critics' assertions that the bill was merely symbolic.

Coretta Scott King, widow of the late civil rights leader and co-chairman of the coalition, said the goal set by the legislation - trimming unemployment to 4 cent by 1983 - was a viable one, and warned that President Carter will be "in serious trouble" if he fails to achieve it.

At the same time, however, the spokesmen conceded indirectly there was no way to require the administration to adopt the policies needed to reach the 4 per cent goal. The only way to enforce the measure, one spokesman suggested was to "beat" Carter "at the polls."

The statement by the council marked the first formal defense of the [WORD ILLEGIBLE] of the bill was made public by the White House last week. The new legislation was worked out in months of negotiations between its sponsors and top administration aides.

The measure has been widely criticized on two grounds.First, that the 1/2 per cent target cannot be achieved without exacerbating inflation, and second, because the bill contains no mechanism for putting the policies into effect that would achieve the job goal.

However, Murray H. Finley, president of the Amalgamated Clothing and Textile Workers Union and co-chairman of the coalition along with Mrs. King, dismissed the initial reaction as "early criticism" delivered "before an analysis had been made."

Finley called the 4 per cent unemployment goal "a reasonable figure for a reasonable date to be achieved. The major economic problem facing this country today is jobs," he said. "The legislation is long overdue. Its time has come."

In a major concession, the sponsors admitted that in order to achieve the 4 per cent target, Carter "May have to postpone" another of his major economic goals - the balancing of the federal budget. The President had promised to eliminate the deficit by 1981, but has backtracked recently.

Liberals had hoped Carter's endorsement of the jobs legislation would force him to abandon the budget-balancing goal, which many regards as a restraint on how rapidly he can move to reduce unemployment. The jobless rate now is 7 per cent of the work force.

Coalition spokesmen predicted that with Carter's formal backing the measure most likely would pass in the next session of Congress. Ken Young, a legislative expert with the AFL-CIO, said supporters were "optimistic" that the bill would become law next year.

In a separate development yesterday, William A. Cox, an economist for the congressional Joint Economic Committee, predicted that the jobless rate would fall to about 3 per cent by the late 1980s without any additional job-creation measures because there will be proportionally fewer teenagers in the labor force.

Cox told a group at the University of Southern California that one of the reasons for the high unemployment rate now is the number of young people in the population, a group with a chronically high jobless rate. But their numbers will be reduced by the tapering off in the World War II "baby boom," he said. "A decade from now, they will be absorbed much easier."