Iran and the United States began new talks yesterday on a long-stalled nuclear cooperation agreement that could involve a multibillion-dollar purchase of American nuclear power plants.

The talks have been in suspension since last August. The disagreement centered on American terms for safeguards to prevent the spread of nuclear weapons, including opposition to any nationally controlled nuclear fuel reprocessing plant. The United States advocated regional reprocessing centers.

Iran subsequently has publicly disclaimed an intention to have a nuclear reprocessing plant, and has indicated that its prime interest is an assured supply of nuclear fuel, administration sources noted yesterday.

American officials said the prospects now appear good for moving toward a nuclear accord.

Two years ago Iran expressed interest in purchasing up to eight American nuclear power plants, as part of its program to acquire more than 20 plants from various countries by the end of this century. It now has contracts with West Germany and France for each to provide two plants.

Administration officials said that they hope to establish the basis for a nuclear cooperative agreement in the present meetings, but that final action will await pending congressional legislation to improve safeguards on nuclear exports.

Akbar Etemad, president of the Iranian Atomic Energy Organization, leads his country's delegation in the discussions covering all forms of energy, under the united States-Iranian Joint Commission Robert W. Fri, acting administrator of the Energy and Development Administration, heads the U.S. delegation which includes State Department officials.

The talks are scheduled to end Wednesday.