Frustrated by U.S. laws that have blocked the sale of two large atomic reactors to China, Westinghouse Electric Corp. is seeking Reagan administration permission to sell Peking $20 million worth of components for a smaller nuclear power station to be built by the Chinese.

According to documents filed with the Nuclear Regulatory Commission, Westinghouse has applied for an export license to sell a variety of pumps for Peking's "728 project," a 300-megawatt nuclear power plant on Hangzhou Bay not far from Shanghai.

But NRC officials said yesterday that the equipment Westinghouse is proposing to sell includes two primary reactor coolant pumps, which cannot be exported to China under the 1978 U.S. Nuclear Nonproliferation Act until the two countries enter into an agreement of nuclear cooperation.

Since China shows no inclination to agree to international nonproliferation safeguards on its nuclear facilities, which the U.S. act requires, this attempt by Westinghouse appears likely to be no more successful than its earlier bid to sell Peking two 900-megawatt reactors.

"It's the same problem," said James V. Zimmerman, assistant NRC director for exports. "These are major components of a reactor, so they are being treated the same as if the application was for a reactor itself. We've shipped the application over to the State Department."

State Department officials indicated it is unlikely that any change in the U.S.-Chinese relationship would occur before the March 1 deadline that Peking set for Westinghouse to obtain the export license.

China is one of the few countries that appears to have a budding atomic power program. But sales efforts by Westinghouse and other U.S. firms, including Borg Warner, have been hampered by charges that China is providing assistance to nuclear programs in Pakistan, Argentina and South Africa.

All three are suspected of trying to develop nuclear weapons and are ineligible to receive U.S. nuclear technology or equipment because they refuse to put all their atomic facilities under international safeguards.

Jiang Shengjie, an official of the Chinese Ministry of Nuclear Industry, said during a recent visit to Washington that Peking intends to seek commitments from countries to which it sells nuclear materials that they will be used exclusively for peaceful purposes.

He was not willing, however, to discuss China's refusal to submit to international inspection of its own nuclear facilities, currently used almost exclusively for nuclear weapons production.

Chinese sources recently have resumed hinting that they will probably turn to a French-British consortium for the two 900-megawatt reactors that Westinghouse had hoped to build in Guangdong Province near Hong Kong.

"It looks as though the Chinese are about to give up and turn to the French on that one," said former ambassador Dwight Porter, who is now Westinghouse's representative here.

But Porter said Westinghouse continued to hope that the Reagan administration would find a way to approve its application to sell China parts for the smaller indigenous reactor. In addition to the two primary reactor coolant pumps, Westinghouse is seeking to provide centrifugal charging pumps and an in-core flux mapping system for the Chinese reactor.

"For Westinghouse, participating in the 728 project would establish an important political and commercial tie with China," Porter said. "It would mean in effect that this could represent a continuing relationship between China and the United States in the nuclear field."

By blocking the sale of civilian atomic power equipment to China, the Nuclear Nonproliferation Act appears to lock the administration into "what seems to me a very, very stupid foreign policy," he argued. "China has had a nuclear weapon now for 25 years. It has 15 production reactors for plutonium, and it recently tested a delivery system which was a submarine-based ICBM. Now it's getting around to deciding it needs commercial nuclear power.

"Westinghouse really does not see the same nonproliferation issues with China that you might be concerned about with a Pakistan," Porter added.