President Reagan, in an action with major implications for proliferation of atomic weapons abroad, yesterday reversed the policies of Presidents Ford and Carter regarding the domestic reprocessing of nuclear fuel.

Ford had temporarily disapproved and Carter had indefinitely banned commercial reprocessing operations at home to discourage other nations from pursuing this path abroad. Reprocessing of spent nuclear fuel is a longstanding method of producing plutonium, the raw material of atomic weapons.

Reagan, in a new government policy strongly backing nuclear power development, disclosed that he is lifting the existing ban. Energy Secretary James B. Edwards, announcing the new program, said the government is studying ways to encourage commercial reprocessing by providing financial incentives.

Officials of the State Department and the Arms Control and Disarmament Agency described the new policy as domestic in origin and orientation. The officials said it flowed logically from Reagan's July 16 policy regarding nuclear weapons spread abroad which said that the United States will no longer inhibit civil reprocessing on the part of advanced nations "where it does not constitute a proliferation risk."

Officials in the foreign policy field said a U.S. overseas policy regarding reprocessing in nations without nuclear weapons is still incomplete.

A spokesman for the Department of Energy said the considerations behind yesterday's shift "did not go into the question of proliferation abroad." The spokesman said that in that department's view, domestic policy and foreign policy regarding nuclear fuel reprocessing are separate matters.

Edwards, who was named by Reagan to coordinate efforts to "streamline" nuclear power regulation, called the new program "a logical step to development of advanced nuclear reactors."

It has not been decided, according to Edwards, whether the plutonium that may be produced by commercial reprocessing operations will be acquired by the government for making nuclear weapons. Because of sharp increases in nuclear weapons production, the government is reported to be running short of plutonium.

Reagan's policy statement, which has been in preparation for several months, also called for completion of the Clinch River breeder reactor in Tennessee. Carter had halted construction of the plant and opposed development of breeder reactors because of the possible contribution to the spread of nuclear weapons abroad.

The Reagan plan also called for working swiftly toward "deployment of means" to solve the nuclear waste problem, which has been a major inhibition to nuclear power development. Reagan's statement called nuclear power "one of the best potential sources of new electrical energy supplies in the coming decades."

Edwards estimated that under speeded-up regulations, the Nuclear Regulatory Commission hopes to license 33 nuclear power plants in the next two years, an unprecedented number.

Criticism of the presidential program was quick in coming. Rep. Edward J. Markey (D-Mass.) called the policy "nuclear boosterism and government intervention to aid the sagging nuclear industry." Markey, whose House Interior subcommittee has scheduled hearings on the Reagan policy, said one result of the program will be "the production of tons of lethal plutonium which can be diverted to nuclear bombs even by unsophisticated terrorists."

Richard Udell, speaking for a Ralph Nader affiliate, Critical Mass, called Reagan's program "incredibly irresponsible" from public health and economic standpoints. He said the reversal on commercial reprocessing will make it "difficult if not impossible" for the United States to restrain the reprocessing activities of foreign nations.