Behind barbed wire and guarded gates, teams of Western-trained scientists are quietly but relentlessly nudging Taiwan into the nuclear arena.

Anxious eyes in both the East and the West are watching the Institute of Nuclear Energy Research, a sprawling concrete complex southwest of Taipei that shelters Taiwan's nuclear pursuits. Established in 1970, the government-supported insitute is a branch of Taiwan's Atomic Energy Council. Here, the Nationalist Chinese have assembled all the facilities needed to reprocess spent nuclear fuel and produce plutonium that can be used to develop nuclear arms.

Ensconced in the Taiwan institute is a 40-megawatt Canadian-supplied research reactor closely resembling the reactor that was instrumental in India's 1974 development of its first nuclear device.

Although they have the required paraphernalia, the Nationalist Chinese periodically repeat this vow not to manufacture nuclear weapons, thus reminding the world that they can do so if they want to.

President Carter's Jan. 23 statement favoring elimination of all nuclear testing was followed by a statement of support from Taiwan Premier Chiang Ching-kuo. Chiang added that "although the Nationalist Chinese government has the capability of developing nuclear arms, it will never engage in the production of such weapons."

In 1975, the premier said his country would never develop nuclear weapons because the prospect of unleashing nuclear fury against "Chinese compatriots on the mainland" was unthinkable.

The Nationalist Chinese face other pragmatic considerations. A survey conducted by the International Institute for Strategic Studies in London estimated that the People's Republic of China has a stockpile of 200 to 300 atom and hydrogen bombs. Said one Taiwanese official, "What good is it if we have 10 bombs when the aggressor has 100?"

Another analyst said that although Taiwan has the expertise to develop a nuclear device, the Nationalists have not yet perfected an effective delivery system. "At this point," he said. "If Taiwan stockpiled plutonium or even detonated a nuclear test device, it would be like playing with gunpowder without a gun. And you don't throw gunpowder all the way to Peking."

This last point may not remain a consideration for long. Taiwan's Institute of Nuclear Energy Research is conveniently adjoined by the top-secret Chung Shan Military Research Institute, believed to be supported by Taiwan's Ministry of National Defense. An informed source said that the Chung Shan Institute specializes in programs involving projectile guidance systems missile desing and tracking, rocket fuels, and nuclear warhead research.

Prof. Victor Cheng, secretary general of Taiwan's Atomic Energy Counci, said, however, that the Chung Shan Institute's highly classified research is for "defense purposes only" and that the institute is not dealing with nuclear warheads.

Nonetheless, the Institute of Nuclear Energy Research and the Chung Shan Institute cooperate on some projects and sare some common facilities, including a library and an advanced-design computer. In 1975 a news magazine report quoted a U.S. expert on Taiwan's nuclear developments as saying that Taiwan's nuclear warhead delivery research program was being conducted by "programming experiments on computers - the way the Israelis do."

As they progress toward the final nuclear step, however, the Nationalist Chinese are restrained by the fact that their budding but commercial nuclear power generation program is dependent on U.S. hardware.

The state-owned Taiwan Power Co. has embarked on a multibillion-dollar program to reduce dependence on imported oil by constructing three nuclear-power plants. They would double Taiwan's present installed power capacity by 1985. The company's first commercial reactor is to begin operation this year. Each of the three plants will house two reactor-generator units and their combined power capacity will be 5.142 megawatts. All major equipment and most fuel for the units has or will come from the United States.

Taiwan also relies on the United States for crucial fuel enrichment service that are insured by a 30-year contract between the Taiwan Power Co. and the U.S. Energy Research and Development Administration.

The United States also supplies massive loans to Taiwan Power Co. Construction cost alone for the three nuclear plants is estimated at more than $2.7 billion. Of this sum, $1 billion reportedly has been lent by U.S. banking institutions. The largest source of funds is the U.S. Export-Import Bank, which has lent the power company more than $900 million for nuclear and other projects. The Taiwan Power Co. is the bank's biggest single loan customer.

These factors have no doubt discouraged Taiwan from nuclear-weapon work. Although the Nationalist Chinese intended originally to reprocess spent nuclear fuel and even constructed a reprocessing laboratory, Premier Chiang's recent "no-reprocessing" vow implies that the facility will never be used. The modest reprocessing lab was completed in late 1975.

Officials here say it has not even been tested, because Washington never gave its final consent.