TAIPEI, Taiwan (AP) _ Thousands of people gathered in a schoolyard one recent Saturday night and heard speakers condemn the Nationalist Party that has ruled Taiwan since 1949.

Until recently, that sort of thing would not have been tolerated.

Such dissident rallies, as well as non-political protests, have become common in recent months.

Observers say this new turn on this island of 19 million people stems from the successful formation last year of an opposition political party, the government's restrained response to displays of dissent and plans to scrap the martial law that has been effect for 38 years.

A ranking police official, speaking only on condition of anonymity, said that many more demonstrations have been held but he refused to be more specific.

Political dissidents claim they have organized 52 rallies since January, 1986, while roughly 50 other rallies have been reported, ranging from protests against environmental pollution to demonstrations for school reforms.

Among recent protests:

-Newly elected dissident lawmakers punched and shoved Nationalist legislators at the February opening of the Legislative Yuan, Taiwan's highest lawmaking body, over procedural matters. They also organized noisy street demonstrations to protest martial law.

-About 70 students from the National Taiwan University staged a sit-in outside the Legislative Yuan on March 24 to demand university reforms and less interference by military and party officials at school.

-About 60 aborigines demonstrated in Taipei nine days later to protest a plan to build tourist hotels on their tribal graves in central Taiwan.

A few of the demonstrations were violent but there have been no serious injuries.

Scholars say the government fears a crackdown on rallies will increase support for dissidents, who formed the Democratic Progressive Party in September in defiance of martial law, which prohibits new political parties.

The Democratic Progressive Party received 21.6 percent of the vote in a December election for Legislative Yuan seats. The Nationalist showing was 67.5 percent and the remaining votes were cast for independents.

But the government has said it has adopted a ''tolerant attitude to avoid triggering confrontation or bloodly rioting.''

Yang Kuo-shu, director of the psychology department of the National Taiwan University, believes the dissidents should receive credit for people's readiness to speak out.

Dissidents have ''shattered the taboo on demonstrations and contributed to a thawing of the political atmosphere so that people now think demonstrations are OK as long as no violence erupts,'' Yang said in an interview.

''Our requests for change were turned down many times by school officials. ... So we have turned to demonstrating off campus,'' explained Lin Chi-wen, a National Taiwan University student when asked about the March demonstration for school reform in which he participated.

Another reason for the increase in demonstrations is President Chiang Ching-kuo's announcement in October that martial law will be replaced by less rigid security regulations. He has said lifting martial law was part of the movement toward democracy.

Under martial law, military officials can ban any rally, domonstration or parade deemed a threat to the security of Taiwan, which says it still is at war with the Communist government of mainland China.

The Nationalists, who fled the mainland for Taiwan after their defeat by the Communists in 1949, still claim to be the legitimate government of China.

Dissidents are moving with some caution, however, concerned that mass rallies posing a stronger challenge to the government's authority could turn into a bloody riot.

They were split over whether to hold a demonstration April 19 in front of the Presidential Office Building to demand that martial law be lifted quickly and that no substitute security regulations be enacted.

Organizer Chen Shui-pian told a news conference that the rally was called off to avoid a split among dissident leaders.

He said many of the 13 Democratic Progressive Party lawmakers opposed staging a rally while they still have time to argue their case against the security regulations in the Legislative Yuan.

But dissident party Chairman David Chiang vowed that his group would call a mass rally if the Nationalists use ''railroad tactics'' to push their proposals through the legislature.