SINGAPORE >> The ruling People’s Action Party led by Prime Minister Lee Hsien Loong was returned to power on Sunday with a majority of 60 percent of the vote after a hard-fought parliamentary campaign in which opposition parties made their strongest inroads since Singapore’s independence in 1965.

The opposition was contesting all but one constituency for the first time, drawing enthusiastic crowds, many of them energized by Internet campaigning that opened the race to a clamor of voices and points of view in this tightly controlled city-state.

In a significant upset, a five-member Workers’ Party slate won a group-candidate constituency over a ruling party slate that included two Cabinet ministers. The results assured the opposition of its largest representation in Parliament in history.

One other member of the Workers’ Party was also elected, meaning that the ruling party will hold 81 seats to the opposition’s six.

The popular vote was also a concern for the ruling party. It received just over 60 percent of the ballots cast, the lowest in its history, down from 67 percent in 2006 and 75 percent in 2001.

“We understand that this was a watershed election,” said the prime minister, who promised to study the outcome and listen to the voters.

The People’s Action Party, or PAP, has never been out of power, and until 1981 there were no opposition members of Parliament. Until this election, there had never been more than four members from opposition parties. The ruling party’s loss of seats was its biggest since independence.

“A new chapter has opened in Singapore’s history,” said the foreign minister, George Yeo, one of the cabinet ministers who lost his seat. “There was a tide we could not overcome.”

In the last election, in 2006, the opposition put up candidates in only about half the constituencies, winning just two parliamentary seats. This year, candidates for six opposition parties contested 82 of 87 seats.

As public counting of the votes ran deep into the night, constituency by constituency, it became evident that many opposition candidates had made strong challenges even in constituencies they had lost and that the overall percentage of votes won by the ruling party was declining.

The ruling party faced voter discontent over inflation and a growing imbalance of wealth as well as resistance to an influx of foreign workers. The online campaigns gave new voice to public discontent over the PAP’s monopoly on power.

In what seemed an attempt to embrace the future, Singapore loosened its grip on political discourse in the unruly world of the Internet.

Government opponents are often sued for defamation and public speech has been permitted only in a small park called Speakers’ Corner (which was shut down during the campaign), but experts say the new opening, if only in the virtual world, appears to be a redefinition of what are known here as “out-of-bounds markers.”

Following changes to the Constitution and election laws, campaigning is now permitted throughout cyberspace — in podcasts, videos, blogs, instant messaging, photo-sharing platforms like Flickr, social networking sites and electronic media applications found on cell phones.

For the first time, campaign recordings could be posted as long as they were not “dramatized” or published “out of context.” Video taken at an election rally could be uploaded onto the Web without being submitted to the Board of Film Censors.

“Social media have lowered the barriers of entry into political discourse everywhere,” said Mark Cenite, an assistant professor of communication and information at Nanyang Technological University. “But that’s particularly significant in Singapore because here the barriers to entry into political discourse and the accompanying risks have been so high.”

Despite the changes to Internet regulations, demonstrations and public speech still require permits. Political speech is restricted to candidates. Opposition politicians and the news media face the possibility of defamation suits. The mainstream news media are tightly controlled and have not acted as a check on the government, experts say.

During the last parliamentary campaign, in 2006, a small number of current-events blogs were the main forum for online citizen participation. Political speech was technically illegal and demanded a greater level of risk and commitment.

“Now that the barriers to entry to political dialogue have fallen, the effect has been electric,” Cenite said. “Government critics are able to easily identify and support one another without making a headlong commitment to politics and take the accompanying risks.”

All of this has contributed to an intense campaign in which opposition parties — which now hold just two of 84 elected seats — are drawing bigger crowds to rallies, fielding more candidates and, in contrast to the past, contesting all but one constituency. In the last election, opposition parties contested just half the constituencies.

The campaign itself was been transformed as social media give smaller, poorer parties a wider audience, bringing greater inclusiveness and competitiveness to political debate.

Rather than trying to suppress online political organizing, as China and Vietnam have done, Singapore has taken a gamble on making it part of the legal campaign system.

“I don’t think they had a choice,” said Kin Mun Lee, known on his blog as Mr. Brown, who said he skirted the law in the last campaign by avoiding explicitly political comments. “Before, it was a very limited kind of provision for online speech. Definitely they had to change the rules because of the proliferation and availability of options.”

© 2011 The New York Times Company