Three unions and a coalition of environmental groups yesterday called for the renewal of federal funding for a controversial radiation researcher who lost his government grant when he discovered elevated cancer levels in workers exposed to low-level radiation.

In separate letters, the Machinists, Steelworkers and the Oil, Chemical and Atomic Workers unions, along with a coalition of 10 environmental groups, called on Health, Education and Welfare Secretary Joseph A. Califano to resume fundidng for the work being done by Universty of Pittsburgh epidemiologist Dr. Thomas Mancuso.

Mancuso lost his federal research grant in 1976 after he discovered elevated cancer level in workers at the government's nuclear facility at Hanford, Wash.

According to Energy Department documents released late last year to Mancuso under a freedom of information request, the Atomic Energy Commission, which paid for the study, was seeking material to rebut possible claims from workers suffering radiation damage at government facilities.

The documents indicated that when Mancuso's findings showed potential low-level radiation dangers to workers, the Energy Research and Development Administration that succeeded the AEC dropped its funding for the work. Mancuso has continued the study with smaller private grants.

The letters, which were released to the press yesterday, are part of a coordinated effort by the unions and environment groups to push the Energy Department out of nuclear safety research because of alleged conflicts of interest.

"As long as DOE is involved... a conflict will exist and health concerns can be expected to be compromosed with the departmnet," Steelworkers official John J. Sheehan wrote to Califano. The HEW secretary is heading an interagency task force ordered to look into low-level radiation dangers last year by President Carter.

An HEW spokesman said yesterday that the letters had not yet reached Califano. Other officials said Mancuso was contacted last week by the National Institute for Occupational Safety and Health and urged to submit a new research grant application.