SAN JOSE -- For years, Cong Thanh Do waged his battle for democracy in Vietnam on a laptop computer in his quiet suburban home, thousands of miles from the country he fled a quarter-century ago.

No one -- not even his wife or three kids -- knew the soft-spoken Silicon Valley engineer had founded an underground political party, advocated for jailed dissidents or penned dozens of pro-democracy essays -- all under the pseudonym "Tran Nam."

Do's secret life as a freedom fighter was revealed to his family and the world when he was arrested while vacationing in Vietnam and accused of plotting against the communist government. He spent more than five weeks in detention, staging a 38-day hunger strike while a slew of American politicians and activists demanded his release, before he was deported to the United States last month.

Though Do, 47, says he prefers working behind the scenes, since returning to California he has embraced his new celebrity to advance his cause: bringing democracy and political freedom to Vietnam. He said his imprisonment illustrates why the country's one-party system needs to change.

"The government lets you have freedom in the stomach, but they control your ideas," Do said during an interview in his modest house in San Jose. "As long as you accept the rules, it's OK. But if you want to stand up for your rights, you're going to be in trouble."

The Vietnamese Embassy in Washington, D.C., did not respond to calls seeking comment on Do's case.

Do's wife and children said they never suspected their husband and father had led a double life. Over the past five years, he spent several hours each night typing away at the dining room table. His family thought he was just working on engineering projects or surfing the Web.

"I didn't have any idea," his wife, Tien Jane Dobui, 43, said, sitting next to Do in their living room, where jade art pieces, porcelain vases and family photographs decorate the walls and shelves. "I wasn't angry at all. I was just surprised he was so deeply involved in politics."

Do, a naturalized American citizen, said he didn't tell the people closest to him to protect them. He worried that if his identity were uncovered, it would endanger him, his family and the People's Democratic Party, the outlawed political group he co-founded last year to promote free elections and human rights in Vietnam.

"To live a better life, to have freedom and democracy for all, we the people have to stand up," Do wrote in the party manifesto.

Vietnam's fast-growing economy has raised incomes and lifted millions out of poverty in recent years, but critics say the country hasn't done enough to improve its human rights record. Activists hope President Bush will push Hanoi to hasten political liberalization when he visits in November.

Seeing no future in communist Vietnam, Do and Dobui fled in a small boat in 1981 and eventually settled in California, where he studied to be an electrical engineer while working nights as a janitor.

Over the years, he created a comfortable middle-class life for himself and his family, but he never forgot his roots. In the early 1990s, he began working with other Vietnamese refugees to push for political change back home.

"Even though I have lived here so long, part of me is still Vietnamese," Do said. "I want to see the Vietnamese people enjoy what I enjoy here -- freedom and democracy."

Four years ago, Do began corresponding by e-mail with political dissidents inside Vietnam and launched the Democracy Club, which provided information on jailed activists to groups such as Amnesty International and Human Rights Watch. Using the Tran Nam alias, he wrote and edited an online newsletter that advocated political freedom and reported the inside workings of the Communist Party.

Do and other club members last year founded the People's Democratic Party, one of numerous political groups calling for regime change and democratic reform in Vietnam.

Unlike other exile groups, Do's Web-based party is focused on building membership inside the country. He said the party has "hundreds" of members, 90 percent of whom live in Vietnam. Party members communicate almost exclusively by e-mail and use pseudonyms to protect their identities.

"If you want to have a positive effect, you have to be inside, not outside," Do said. "Without the Internet, we wouldn't be able to form the party."

Do was visiting Vietnam with his wife and 9-year-old son when he was arrested on Aug. 14 in Phan Thiet, a coastal city north of Ho Chi Minh City.

He believes Vietnamese authorities had been tracking members of his party and began following him after he met with two other leaders at a restaurant several days before his arrest. The men, both Vietnamese citizens, were arrested the same day and remain imprisoned, Do said.

Police took him to Ho Chi Minh City and accused him of being a terrorist with a plan to bomb the U.S. consulate -- allegations Do and American officials have denied.

"They tried to make me admit I'm a terrorist, but I denied it all the way," Do said.

After he was transferred to a state prison, he shared a cramped, airless cell with two convicted felons. He said he was interrogated two or three times a day about the People's Democratic Party by officers demanding the identities and e-mail addresses of its members.

To protest his arrest, he went on a hunger strike, only drinking water, milk, lemonade and rice powder for 38 days. Sick and weak, Do spent most of his time lying on the floor and meditating while his cell mates cared for him. Still, he said he refused to disclose the party's secrets even while his requests to see U.S. consulate officials were denied.

"When you're on a hunger strike and nobody knows it, it's tough," Do said. "Because I worked underground for so long, even my wife didn't know why they arrested me."

On Sept. 1, he finally met with American officials and revealed that he was the online activist Tram Nam -- a disclosure that shocked them and his family.

Do's son, daughter and wife scrambled to learn about his democracy work, searching his computer files and talking to activists who only knew him as Tran Nam. They set up a Web site, worked the phones and testified at a congressional hearing on human rights in Vietnam.

Do's detention angered Vietnamese Americans who fled their homeland after the Vietnam War and were outraged its authoritarian regime would arrest a U.S. citizen advocating nonviolent political change.

"This case was a rude awakening for the Vietnamese American community," said California Assemblyman Van Tran, R-Garden Grove. "He's an American, and he gets this type of treatment? What does it say about the native Vietnamese and how they're being treated?"

Three weeks after politicians ranging from Gov. Arnold Schwarzenegger to Sen. Dianne Feinstein began calling for his release, Do was put on a plane to San Francisco, where he was greeted by his family and a crush of reporters.

"I'm really proud of him," said his son Vien Dobui, 24. "It takes a lot of courage to do something that puts yourself in danger for other people."

Regaining his health after the hunger strike that left him 20 pounds lighter, Do is back to his democracy work, meeting with activists who knew him by his alias and campaigning for the release of six party members he says are still being held by authorities in Vietnam.

Do said he probably won't be allowed back in Vietnam for years, if ever, but he doesn't plan to quit pressing for change in his native land.

"This is not going to stop me from spreading democratic values in Vietnam," Do said. "I plan to keep on fighting as long as possible."