Hsu Rong-su hardly seems like the kind of politican who is threatneing enough to unite old enemies against her. She is far from an oratorical spellbinder, champions no burning issues and has no political machine.

Yet, Hsu, a freshman member of the National Legislature, is regarded as a dangerous political influence by rival governments that agree on almost nothing else -- the Communist leaders of mainland China and the Chinese Nationalists who run in this island of 18 million people.

Hsu is one of a small but growing number of native Taiwanese who have recently entered political life and in effect oppose the goal of reunification that still is the sacred mission of both the Communists in Peking and the Nationalists who fled here from the mainland 32 years ago.

Native Taiwanese who form 85 percent of the island's population are ethnically Chinese, but they have been cut off from the mainland for almost 100 years and consider Taiwan ther ancestral home. They are known here as "local people" while the former mainlanders are called "outside the provinces" Chinese.

Although the "locals" have been subordinated by the Chinese Nationalist minority for three decades, their dominance of the island's economy and their recent political activism have suddenly turned them into a domestic political force and an important -- some say vital -- factor in the sticky reunification issue.

Communist China, fearing the political emergence of separatist-minded Taiwanese after the powerful Nationalist old guard dies off, have sought in recent years to start a dialogue with their old foes by offering a raft of political guarantees and incentives.

The most recent Communist proposal which came at the end of September, was to include Nationalist officials in the leadership of a reunited China. It was believed to be at least partly motivated by worries of a Taiwanese takeover after the death of President Ching Ching-Guo who is 72, and reported to be suffering from diabetes.

Nationlist officials who view Taiwanese activists as a challenge to their rule and an unwanted source of pressure on the sensitive reunification question have responded to their political opposition alternately with repressive force and conciliatory gestures.

At least for the time being, Taiwan activists and the Chinese Nationalist leaders agree on mainland policy. Taipei has consistently rebuffed the Communist overtures as tricks and pledges there will be "no negotiation, no compromise, no contacts" until the Peking authorities disclaim Marxism.

Vice Foreign Minister Frederick F. Chien reflected the feas both of the Nationalist government and the Taiwanse majority when he said in an interview last week that Peking's latest proposal was unacceptable because "the underlying premise of these overtures is they want us to be a province, a region. They want to reduce our status to that of a local government and they would remain as the central authority."

But most opposition leaders, who call themselves "nonparty" because the Nationalist government refuses to allow them to form a political organization, believe the mainland Chinese here still yearn for their motherland and eventually will make a deal at the islanders' expense.

"We're afraid that the Nationalists will sell out Taiwan," said Hsu Rong-su, a former school teacher who turned politican after her activist husband and dozens of others were imprisoned last year in connection with an antigovernment rally that turned into a riot.

Kang Ning-hsiang, Taiwan's most influential "nonparty" leader, who sits in the National Legislature and publishes two opposition magazines, was unsually blunt when asked what Taiwanese would do if the Nationalist leadership began negotiations with the mainland Communists.

"We would resist," said Kang, who is considered a moderate "nonparty" leader.

"The Taiwanese don't want to find themselves after 30 years of finally getting near the levers of power only to see another group of Chinese come in and take it away," said an American businessman who has observed Taiwan politics for years.

"If the Communists are doing their intelligence," he said, they know the last thing they'd want is the opposition running this government."

Although native Taiwanese for years have demanded a greater political role to reflect their majority status, Nationalist leaders have refused to give up control. Their justification is that the Nationalists comprise the rightful government of China -- of which Taiwan is just a province -- and that it is temporarily confined to the island until an opportunity arises to retake the mainland.

Nevertheless, Taiwanese have gradually increased their political power in recent years, sometimes with Nationalist approval. In an effort to broaden their political base, the Nationalists have brought thousands of Taiwanese into the party and appointed a few to Cabinet posts, the party's central Executive Committee and top municipal jobs.

Both "party" and "nonparty" Taiwanese also have gained political standing through elections, dominating local government and sometimes forming a majority of active members in the rubber-stamp National Legislature, where former mainlanders who are elected for life more than 30 years ago are gradually dying off or becoming too ill to participate.

Piubicly, Nationalist officials of Taiwan origin stand behind the party's principles, including "recovery" of the Chinese mainland. Privately, however, many are said to believe the task of reunifying the breakaway island with the mainland is impossible.

"Blood is thicker than water," said a Taiwanese intellectual who has contacts with islanders of party stature. "For most of them, being Taiwanese comes before Nationalist."

Opposition politicans dissatisfied with the pace of "Taiwanization" of the government and party have intensified their political activity since 1977 when "nonparty" candidates captured 37 percent of the vote and a significant number of seats in provincial elections.

They raised their total of seats in the National Legislature to 11 last December and hope to gain greater control of provincial and municipal offices through elections next week. "Nonparty" candidates are contesting every seat and leaders such as Hsu and Kang are crisscrossing the island to lend their support.

The independents, who run the ideological gamut from democratic socialism to liberal democracy, draw their support from the Taiwanese middle class, young intellectuals, disgruntled farmers and workers and Taiwanese living in Japan and the United States.

Although almost all "nonparty" activists are said to oppose Taiwan's reunification with the mainland, few see the need to raise the issue now because of the Nationalists' rejection of Peking's initiatives. Many fear reprisals just for discussing the issue publicly.

More outspoken opposition members explain when questioned that they favor "separation" from the Communist nation. But, they stress, they are against prosposal by overseas Taiwanese to turn the island into an independent state -- a concept both the Communists and the Nationalists abhor.

Political observers here believe that maintaining the status quo may also be the best strategy for the island's ruling elite who face conflicting pressures both from the local separatists and from Peking authorites whose gestures make disinterested Nationalists look intransigent.

If Taipei shows the slightest interest in talks with Peking, the government could arouse serious domestic opposition, according to foreign analysts and local political observers. If it gives up its 32-year goal of "recovery," the Nationalists risk the loss of their legitimacy as the rightful governors of Taiwan.

A turn to independence also could invite an attack from the Communists, who consider the island an inalienable part of China.

Continued separation has even become comfortable for many former mainlanders who retain curiosity for their homes but have accepted the idea of never seeing them again.

Nationalist leaders themselves are divided on how to face these conflicting pressures, according to foreign and local observers.

Old-line party conservatives led by Gen. Wang Sheng, 64, the powerful director of political warfare, continued to predict imminent collapse of mainland communism and the Nationalist return. They are said to resist Taiwanization of the government as an act of surrender and regard opposition politicians as traitors who sap the island's strength and motivation.

Recent years have seen the party hardliners make way for a new breed of young, articulate officials mostly educated in the United States who adopt a more realistic view of Taiwan's role in the world and a more moderate approach to Taiwanese demands for reform.

Although they continue to pay lip service to reunification, these so-called technocrats are said to privately assign it secondary importance. Instead, they seek to turn Taiwan into a model of political liberalism and economic dynamism to serve as an attractive contrast to the mainland.

"For millions of us, reunification is the ultimate goal," said the party's Deputy Secretary General Chen Li-An, 44, an MIT educated mathematician. "It might take decades. But what we can do in the meantime is continue to develop this island and have an impact on the mainland that way."