The Labor Department, under pressure from farm groups, overruled warnings from its own medical experts and others and permitted thousands of 10-to-12-year-old children to go to work in pesticide-laden fields last summer, according to federal documents.

The documents, first obtained by Ralph Nader's Health Research Group, show that top Labor Department officials waived certain provisions of the federal Labor Standards Act in August. The waiver according to a Labor Department official, permitted at least several thousand children aged 10 and older to harvest strawberries and potatoes after the crops were sprayed with a variety of potentially dangerous pesticides.

Dr. Peter F. Infante, a senior Labor Department cancer expert, who advised against the waiver in a report, yesterday called the department's decision "unconscionable."

According to the documents, experts from the Environmental Protection Agency and a private consulting firm hired by the Labor Department also warned in letters and reports that there was no assurance that children would not be harmed if they were allowed to work in fields sprayed with pesticides.

Donald Elisburg, the Labor Department official who signed the waiver Aug 18, said yesterday that he had done so because the Labor Department was being pressed by farm groups acting through the courts.

"It was not a particularly happy situation either way," said Elisburg. "We were left without a practical solution. If we didn't do something the courts would have allowed the children to work in the fields with no controls at all."

According to Elisburg, assistant labor secretary for employment, the waiver allowing the children into the fields contained provisions requiring that waiting periods ranging from two to 100 days had to be observed, for children, depending on which pesticides were sprayed on the fields.

But the documents made public yesterday indicate that the Labor Department set the waiting periods without adequate supporting data. Medical experts warned Labor Department officials that little is known about the effect of pesticides on children and that the waiting periods, which were based on adult exposure information, might not be sufficient for children.

The Labor Department also ignored warnings from Clement Associates, a private consultant it hired here, that there was not guarantee the children would be safe from effects of the pesticides and a recommendation from the consultant that all children working in the fields be placed under medical supervision.

"The department felt that we didn't have the resources to do that and if we tried to force medical supervision we would be back in court and the children would have no protection," said Elisburg.

In its report, Clement Associates recommended that additional study be done on pesticide hazards to children and suggested that an interim exposure standard be set by the Labor Department. Instead, the department issued a permanent standard.

"We certainly didn't give the whole thing a clean bill of health," said Jay Turin, a Clement Associate vice president. "They went beyond what we recommended."

According to the documents obtained by the Health Research Group, senior Labor Department officials questioned the validity of the Blement Associates study but decided to use it anyway as the basis for their waiver.

In an interview yesterday, Turin said the study was based on EPA data. But a letter from EPA official Stephen D. Jellinek to a Labor Department official, written before the Clement Associates' study was done, notes that EPA had found no data on which to gauge the effect of pesticides on children. "The agency cannot say what is or is not a safe standard for children simply because there is no data on which to base such an estimation," Jellinek wrote.

According to the documents, other medical experts also expressed Jellinek's concern at a Labor Department hearing held here at the same time.

Labor Department officials also apparently disregarded other warnings against the waiver from Infante, a senior cancer expert in the department's Occupational Safety and Health Administration.

In a June memo to department officials, Infante warned that little was known of the dangers from pesticides on children and advised against the waiver. "There just is no data to support their waiver decision," he said yesterday. "It is bad enough that we send adults into fields to be exposed to chemical pesticides that we known little about. To do that to children is inconscionable."