Small but detectable residues of three pesticide compounds were found in the breast milk of most mothers who participated in a 1975 nationwide test of pesticide levels in human milk, the Environmental Protection Agency reported yesterday.

Use of the chlorinated hydrocarbon dane - that produced the residues has pesticides - dieldrin, heptachlor and chlorbeen severely restricted in the last few years by EPA because they are suspected of causing cancer in humans.

The substances, once extensively used for crop-protection and, in the case of chlordane, for household pest control, are long-lived. But residual levels can be expected to decline in the future as the effects of the restrictions are more fully felt, EPA said.

In a statement accompanying the report on the study, EPA officials said the 1975 milk-pesticide levels were sufficiently low that "no immediate health hazard to either mothers or their newborn children" is posed.

But the officials said that "the possible long-term consequences of these minute amounts are uncertain." They said the women who participated in the study are being informed of the results and the results are being forwarded to the Department of Health, Education and Welfare for review.

The study - described as the largest of its kind ever undertaken - was based on analyses of milk samples from 1,436 nursing women in 150 hospitals in 46 states, chosen to reflect areas of both high and low pesticides usage.

The samples were tested for dieldrin, heptachlor, chlordane, Mirex, heptachlor epoxide (a breakdown product of heptachlor, and oxychlordane a breakdown product of chlordane).

No chlordane or Mirex was found in any of the samples, and heptachlor was found in less than 2 per cent of the samples, according to EPA. But in "extremely small" amounts, dielrin was found in 80 per cent of the samples, heptaclor expoxide in 63per cent and oxychlordane in 74 per cent, EPA reported.

The mean level for dieldrin in the Fatty, part of milk was 164 parts per billion, the report said. For heptachlor epoxide it was 91 parts per billion and for oxychlordane it was 95 parts per billion.

According to a EPA official, dieldrin, chloradane and heptachlor have been banned for most uses including all food crop purposes - dieldrin in 1974 and chlordane and heptachlor in 1975.

Dieldrin and chlordane are now permitted only for underground termite control, the official said, and all three may be used to treat nonfood plants in nurseries and greenhouses.

Mirex used extensively in the South to control fire ants, will be banned after June 30, 1973, according to EPA.

EPA said some of the milk samples were analyzed last year for PCBs, an oily substance used in heavy-duty electrical equipment that has been found to cause tumors and other health problem in laboratory animals. The samples contained PCB levels that "ranged from barely detectable to low parts per million," EPA said said. All the remaining samples are now being tested for PCBs, it was added.

EPA said the samples have also been tested for DDT, BHC, HCB, Lindane and transnonachlor (a breakdown product of chlordane) and that results of these tests will be made public later this year.