Sens. Warren G. Magnuson (D-Wash.) and Adlai E. Stevenson (D-Ill.) have asked the Environmental Protection Agency to provide a detailed report on a 1975 EPA proposal to pay a Mexican hospital to feed known cancer-causing fungicides to Mexican citizens.

The proposal, which never took effect, was designed to yield information on how massive doses of the funficides affect the human thyroid.

The now-defunct plan was revealed yesterday by Newsday reporter Bob Wyrick.

Magnuson and Stevenson, in a joint letter to EPA Administrator Douglas M. Costle, said: "While it is obviously gratifying to note that current top officials 'were outraged to find out that it happened," that the proposal received as much attention as it did within the agency is cause for grave concern.

"It is also dishearening to observe that the project was called off only because the contract proposal was fashioned in a way that require review by a broader number of officials within the EPA than is usually the case."

Magnuson is chairman of the Senate Committee on Commerce, Science and Transportation, and Stevenson is chairman of the Subcommittee on Science, Technology and Space.

The senators asked Costle to provide the committee, by May 18, with a copy of the reseach proposal and a detailed report of the events that led to the proposal's disapproval. They also asked him to provide recommendations "to assure that proposals of this type are never (again) seriously considered."