A panel of prestigious scientists recommended yesterday that the United States minimize the threat of nuclear weapons spread by putting off until the 21st century the use of plutonium and fast breeder power plants that burn plutonium as a nuclear fuel.

At the same time, the panel of 21 scientists urged that the United States continue to develop uranium-and-coal-fired power plants as the best ways to ensure an adequate supply of electricity for the rest of this century. The panel did not choose between nuclear and coal power, except to say that nuclear energy is cheaper and safer in some ways and coal is cheaper and safer in others.

"We see electrical energy coming from a mix of nuclear and coal for at least the next 20 years," said Spurgeon M. Keeny Jr., director of Washington operations for the Mitre Corp. and chairman of the panel financed by the Ford Foundation. "There are social costs to nuclear power but it compares favorably economically and healthwise to coal, even when one considers the possibility of a nuclear accident."

Ford Foundation President McGeorge Bundy emphasized that the panelists who worked on the study for almost two years were deliberately chosen for their middle-of-the-road views on nuclear energy during the last six years of debates among scientists, utility officials, and the public over whether nuclear plants are safe and economical.

"We believed that the nuclear debates suffered from a shortage of dispassionate and disinterested analysis," Bundy said at a press conference held at the University Club. "So we went out and got people who were not sharply and publicly lined on either side of the nuclear question."

Eleven panelists are faculty members at Harvard University, Massachusetts Institute of Technology, Princeton University and Stanford Universtiy. Former Federal Energy Administrator John C. Sawhill served on the panel, as did Secretary of Defense Harold Brown and Deputy Under Secretary of State Joseph S. Nye in their former roles as president of Cal Tech and professor of government at Harvard, respectively.

All 21 panelists met yesterday afternoon with President Carter in the White House, a meeting that was said to signify Carter's approval of the panelists' conclusions and the doublespaced, 418-page report they turned over to him in the Oval Office.

"Their conclusions mesh very nicely with most of our conclusions," a key White House energy aide said yesterday. "There's very little question the country needs both coal and nuclear power to get away from scarce fuels like oil and natural gas for the next 20 years."

The panel identified as the most important issue on nuclear power whether to go ahead with the reprocessing of plutonium from spent nuclear fuel. The panel said plutonium can be used by other countries and by terrorists to make crude but workable atomic weapons.

"There is no compelling national interest to be served by reprocessing," the panel concluded. "There appears to be little if any economic incentive for reprocessing and the most severe risks are the increased opportunities for the proliferation of national weapons capabilities and the terrorist danger associated with plutonium."

The panel pointed out that the kind of uranium used in power plants can never be used to make weapons but that in five out of six cases each country making its first nuclear weapon did it with plutonium reprocessed from spent uranium fuel. Plutonium does not occur in nature. It is a by product of uranium that has burned itself out making electricity.

To make sure plutonium is not spread around the world, the panel recommended "indefinite" deferral of plutonium recycling and of development of the fast breeder atomic power plant that would burn reprocessed plutonium to make still more plutonium.

If followed by the White House, both recommendations would serve to kill the $500 million plutonium reprocessing plant now under construction at Barnwell, S.C., and the $2 billion fast breeder demonstration plant now being built at Clinch River, Tenn.

An estimated $250 million has been spent by private industry on the barnwell plant and $455 million of public and private funds on the Clinch River plant.

Despite the fact that Japan and Western Europe are developing their own fast breeders and plutonium reprocessing plants, the panel said its suggested policy is not isolationist.

"A breeder cannot operate without reprocessing, and reprocessing needs lots of breeders, maybe 20 to 50," said Dr. Richard L. Garwin of IBM's Thomas J. Watson Research Center at Yorktown Heights, N.Y. "Economically, the rest of the world would be better off without the breeder."

To move the world away from plutonium, the panel urged that the United States greatly expand the government-run factories that enrich uranium for power plants to make sure that foreign countries are assured uranium to make electricity for the next 30 years. There are three such factories.

"U.S. government policy should provide the entire world with a clear alternative to a plutonium economy," said panel chairman Keeny. "We should provide adequate enriched uranium to make other countries turn away from wanting their own enrichment facilities, which is another tempting way to make weapons."

The panel suggested that the United States keep research projects alive on plutonium recycling and the breeder "as insurance" against the day in the 21st century when the world begins to run out of cheap uranium. One way to do this, the panel said, is to bury the spent wastes of a nuclear plant together with its plutonium where it could be retrieved at a later date.

The report said the entire world can be supplied with adequate partly because the world's uranium reserves are underestimated.

Dr. Hans H. Landsberg, co-director of Resources for the Future said, "We think there is enough uranium to run the world's nuclear power plants well into the next century."