HO CHI MINH CITY, Vietnam — His bookshelves are filled with the collected works of Marx, Engels and Ho Chi Minh, the hallmarks of a loyal career in the Communist Party, but Nguyen Phuoc Tuong, 77, says he is no longer a believer. A former adviser to two prime ministers, Mr. Tuong, like so many people in Vietnam today, is speaking out forcefully against the government.

“Our system now is the totalitarian rule of one party,” he said in an interview at his apartment on the outskirts of Ho Chi Minh City. “I come from within the system — I understand all its flaws, all its shortcomings, all its degradation,” he said. “If the system is not fixed, it will collapse on its own.”

The party that triumphed over American-backed South Vietnamese forces in 1975 is facing rising anger over a slumping economy and is rived by disputes pitting traditionalists who want to maintain the country’s guiding socialist principles and a monopoly on power against those calling for a more pluralist system and the full embrace of capitalism.

Perhaps most important, the party is struggling to reckon with a society that is better informed and more critical because of news and opinion that spread through the Internet, circumventing the state-controlled news media.