Citing a 128 percent increase in child labor law violations in the last four years, Labor Secretary Elizabeth Hanford Dole yesterday called for first-offense prison sentences for employers who willfully exploit children in the workplace.

Dole, testifying before the House subcommittee on labor standards, outlined a series of legislative proposals to toughen civil and criminal penalties against child labor law violators.

"Unfortunately . . . there can be no doubt that there are employers violating our child labor laws," Dole said. "Indeed, we have witnessed a disturbing 128 percent increase in violations in the past four years. Faced with a shrinking pool of workers, some employers have reacted by reaching into prohibited age groups for new hires or by putting young people to work in unsafe conditions or for hours beyond the limits of the law."

As part of a nationwide crackdown on child labor law enforcement, Labor Department compliance officers found nearly half the employers investigated in two separate inspection sweeps were in violation of child labor laws. The nationwide investigations in March and June concentrated on employers who traditionally hire teenagers, such as those in fast food restaurants, supermarkets and service industries.

Although final results of the June investigations are incomplete, department investigators have found nearly 20,000 child labor law violations in the approximately 6,000 workplaces investigated.

To help combat the problem, Dole called on Congress to raise the maximum civil fine for each violation from $1,000 to $10,000 and to allow imprisonment of employers on the first conviction of willfully violating child protection laws. Employers currently have to be convicted of willfull violations two times before they risk a prison sentence.

In addition, Dole asked Congress to remove the child labor law exemption for outside sales employees. "We have uncovered a number of disturbing instances where children under the age of 16 were employed in door-to-door sales operations," she said. "Many of these children were working late hours in strange neighborhoods, at well below the minimum-wage rate."

In addition to the increased fines, Dole told the subcommittee she is asking for more compliance officers in the fiscal 1992 budget. The department has 1,000 compliance officers. Dole did not say how many more she would seek.