The Labor Department, which for 13 years has avoided issuing sanitation standards for those who hire migrant farm workers, is about to let yet another deadline slip by, farm-worker advocacy groups charged yesterday.

The department has notified the federal court here that it will miss the Feb. 16 deadline agreed to in a settlement two years ago and will need "at least" two more months to complete its standard.

"There have been several clear, dark signals" from the department "that this administration is determined, once again, to discriminate against farm workers by denying them the elementary right to workplace sanitation standards," said Valerie Wilk, an occupational health specialist with the Washington-based Farmworker Justice Fund.

She said the department is also challenging the jurisdiction of the U.S. district court and has declined to answer inquiries about the progress of the standard.

The issue "has been in cold storage" at the department, said Charlie Horwitz, an attorney who has represented the groups in the long-running legal battle over standards for toilets, hand-washing facilities and drinking water for migrant farm workers. Worker advocates first petitioned for such standards in 1972.

Lack of sanitation standards, health professionals say, poses hazards for the workers, for nearby communities and possibly for consumers of fresh produce.

Labor Department spokesman Jack McDavitt said the department is making a sincere effort to develop a standard and one should be issued soon after April 16. "That's the planning right now," he said.

A proposed standard that was the subject of hearings in five cities last summer would require toilets, fresh drinking water and hand-washing facilities in any field where more than 10 workers are employed. It has been estimated that more than 90 percent of workers would be left uncovered by the rule because most work in smaller crews.

McDavitt said the delay was caused by "the complexity and volume of the hearing record" developed during the hearings. He also said the department has lost some experienced personnel working on the issue.

Horwitz charged, however, that the department had intentionally shifted some personnel to other jobs it regarded as more important and had not hired enough staff to meet its responsibilities.