The White House has agreed to let France sell China an American-designed nuclear power plant if China agrees not to extract plutonium from the plant's spent fuel to use in nuclear weapons.

France is still far from reaching such as agreement with China, sources said yesterday, but negotiations between the two countries intensified in recent weeks with the hope that at least a tentative agreement can be reached before the end of the year.

Talks have been underway for at least six months between France and China on the sale of at least one 900,000 kilowatt nuclear power plant. The sale would be made by the French firm Framatome, which licenses the technology to build the plant from Westinghouse Electric Corp., the world's largest supplier of atomic power plants.

Westinghouse itself cannot sell China a nuclear power plant because the Chinese would not agree to sale conditions required by the Nuclear Nonproliferation Act passed by Congress last year. That law requires that the United States be allowed to inspect all nuclear facilities operated by a country asking for an export license, to make sure plutonium is not diverted from spent fuel.

France has no such law, but it needs U.S. agreement to export the technology licensed from Westinghouse. The Carter administration has told France that it will grant export permission only if the French can get China to guarantee that the technology will only be used for peaceful purposes.

China has been reluctant to make such promises, in part because it does not want any foreign eyes "spying" on its nuclear developments. China possesses nuclear weapons and has tested them in the atmosphere.

If France and China agree to terms that prevent plutonium extraction in the absence of inspections, the United States will probably allow the French sale. While final White House approval is based on a more complex set of conditions, the basic stumbling block is the safeguards issue.

Should France fail to get China's guarantee, then the sale of nuclear power to China could come from Canada or West Germany. Both countries are understood to be eager to sell unclear power to China and neither is bound to licensing agreements the way France is to Westinghouse.

The French are understood to have the inside track on the sale, sources said, because the Chinese prefer the Westinghouse nuclear design over the German or Canadian designs. Presumably, China could also buy enriched uranium from France to fuel the plant. It could not from Canada or West Germany.

It is not know whether Energy Secretary James R. Schlesinger discussed the sale on his recent trip to the People's Republic of China, but observers assume he did. What Schlesinger recommended to the White House on the sale, if anything, is not clear.

Opposition to the sale of nuclear power to China has come from the Pentagon and Congress. The Pentagon has opposed the sale on grounds the Chinese can copy reactor, pump and valve designs to produce nuclear-powered submarines.

Some members of Congress oppose the sale of nuclear energy to China because China still tests nuclear weapons and refuses to become party to the Nuclear Nonproliferation Treaty banning the spread of atomic weapons. China has also shown no interest in joining the International Atomic Energy Agency which polices the spread of nuclear weapons among member nations.

China is understood to want to buy one, and probably two, nuclear plants, each capable of generating 900,000 kilowatts. At today's prices, one plant would cost at least $500 million. Just where China wants to locate nuclear power plants is unknown.