When Congress voted last year to let children as young as 10 work as harvest laborers, proponents painted a pastoral scene, worthy of Norman Rockwell, depicting happy farm children gamboling through berry patches to earn a little extra money for a Saturday movie.

Yesterday another set of pictures emerged at the Labor Department, where regulations have been drafted to implement the law. One was a montage of bureaucratic red tape. Another was, as one witness put it, a "portrait of dark-skinned children in the cotton fields again."

The Labor Department, which didn't want the law in the first place, was caught in the regulations were more restrictive than Congress intended and those who claimed they were too lenient.

One pint at issue is whether the 1977 amendment to the Fair Labor Standards Act, which permits the secretary of labor to grant waivers dropping the minimum age for agricultural work from 12 to 10 under certain specific conditions, would allow harvest work by children of migrant workers.

The amendment requires that working children commute daily from their permanent residence, but the regulation defines residence as "the place where the minor normally resides with the minor's parents . . ."

If that place turns out to be a series of migrant labor camps, the door would be wide open to use of 10-year old migrant children in the fields, according to the National Association of Farm Worker Organizations.

In general, according to the National Consumers League and others who attacked the proposals as open to abuse, the proposed regulations would make field labor by 10-year-olds the rule rather than the exception, inviting displacement of adult workers by low-paid children and exposure of youngsters to danger from machinery, pesticides and overwork.

On the other hand, Rep. william Cohen (R-Miane) and the Washington State Farm Bureau - representing potato and berry-producing areas that led the demand for the lower minimum age - complained that the rules were too restrictive.

Contending that potato and berry harvesting in Maine is a family and community affairs that has never been open to abuse, Cohen said growers should not be made to seek individual waivers with evidence in each case that older workers are not avilable.