Taiwan revised its constitution Tuesday to shrink the size of parliament by half, streamline election rules and set difficult standards for any constitutional amendment that would move the island toward independence.

The changes, endorsed by a special assembly, include a requirement that any future amendment be approved by a three-quarters majority in the legislature and then submitted to a national referendum. To pass, such an amendment would require approval of 50 percent of all eligible voters, not just a majority of those voting.

Political analysts in Taiwan said the high threshold would make it difficult to pass changes designed to formalize Taiwan's de facto independence. In that light, the constitutional shifts seemed likely to assuage Chinese leaders, who have expressed fear that President Chen Shui-bian might propose constitutional amendments that would promote Taiwanese independence.

"Unless there is a major change in the political landscape, it will be impossible for constitutional changes to happen," said Phil Yang, a political specialist at National Taiwan University.

On the other hand, the new rules left open the possibility of such amendments if they drew support from a large enough majority of the island's 23 million inhabitants -- a possibility, however remote, that Beijing had sought to close off. Yang pointed out that Taiwanese law allows for other referendums if the government deems Taiwan's ability to defend itself to be in question.

China, which regards Taiwan as a province that must return to Beijing's rule, repeatedly has warned against any politically significant changes to the constitution, saying they could lead China to resort to force. The Chinese government's Taiwan Affairs Office, responding to Tuesday's reforms, declared that China remains "decisively opposed" to any referendums in Taiwan that would advance the cause of independence.

The constitutional reforms were approved by Taiwan's 300-member National Assembly, an electoral college that was chosen in voting last month expressly to ratify the reforms. The changes, which were endorsed last year by the Legislative Yuan, or parliament, were approved Tuesday with 249 votes, easily topping the required three-quarters majority.

The revised document lowered the number of Legislative Yuan members from 225 to 113 and changed the island's voting rules to lower the chances of small parties gaining seats. The result, analysts said, was likely to be increased dominance by Taiwan's main parties, Chen's Democratic Progressive Party and the chief opposition group, the Nationalist Party.

The clout of smaller parties with minority agendas could be reduced, they added, perhaps increasing efficiency in the Legislative Yuan, which is often deadlocked. As a result, the Taiwan Solidarity Union, which pushes for swift moves toward independence, and the People First Party, which advocates reunification with China, opposed the reforms.

Special correspondent Tim Culpan in Taipei contributed to this report.