Calling environmental damage a global issue, the MacArthur Foundation has granted $15 million to a new Washington-based "think tank" that aims to influence resource policies on an international scale.

The non-profit Institute for World Environment and Resources Inc. will issue studies and policy recommendations on such global problems as plant and animal extinction, erosion, pollution and the accelerating loss of farmland, according to John E. Corbally, president of the John D. and Catherine T. MacArthur Foundation in Chicago.

The board of the new institute is weighted with influential scientists, attorneys, academicians and officials from the Nixon, Ford and Carter administrations. They include James Gustave Speth, chairman of the Council on Environmental Quality under Carter; Russell E. Train, Nixon's CEQ chairman and a former Environmental Protection Administration chief; former defense secretary and World Bank president Robert McNamara, and Matthew Nimetz, former undersecretary of state for security assistance. Speth, a Georgetown University law professor, will be president of the institute.

Members said yesterday the group will remain strictly nonpartisan, avoiding confrontation with the Reagan administration and looking well beyond U.S. borders.

Corbally outlined several environmental threats the group hopes to address: destruction of land by overgrazing and other agricultural problems, consumption of land by suburban sprawl, and accelerating extinction of plants and animals.