SAN FRANCISCO – A Cambodian-American accountant was arrested yesterday on charges he violated American law by leading a militant group that has sought to overthrow the Cambodian government.

Yasith Chhun, 48, of Long Beach, Calif., was indicted Tuesday on charges of conspiracy to commit murder overseas, conspiracy to damage property overseas, and mounting a military expedition against a friendly nation.

If convicted, Mr. Chhun, the American-born president of the Cambodian Freedom Fighters, could face a life sentence on each of the three felony counts. One of the laws Mr. Chhun is charged with breaking is the Neutrality Act of 1794. It prohibits Americans from mounting a military campaign against a foreign country in the absence of a declared war.

Mr. Chhun and his wife, Sras Pech, 39, were also charged in a separate indictment with preparing false income tax returns. The pair is expected to appear in federal court this afternoon for a detention hearing. An attorney for Mr. Chhun, Leonard Matsuk, declined to comment for this story.

From his accounting office in a Long Beach strip mall, Mr. Chhun and his allies have spent years openly fighting for the downfall of Cambodia’s leader, Samdech Hun Sen, who holds the title of prime minister. The State Department and international observers have questioned the elections that put Mr. Hun Sen and his Cambodian People’s Party in power. The State Department has consistently described Cambodia’s human rights record as “poor.”

On November 24, 2000, Mr. Chhun’s group orchestrated an armed assault by about 70 rebels on government buildings in Cambodia’s capital, Phnom Penh. At least four people were killed before the putsch was put down by government forces.

The prosecution of Mr. Chhun, prompted in large part by that unsuccessful coup, draws attention to the awkward intersection between two of President Bush’s top foreign policy goals: fighting terrorism and promoting democracy.

A congressman who has met repeatedly with Mr. Chhun’s group expressed concern yesterday that the prosecution could discourage Americans from working to upend tyrannical regimes. “Unless they can show these guys have been planning some kind of terrorism, meaning attacks on civilians, this is wrongheaded,” said Rep. Dana Rohrabacher, a Republican of California.

Mr. Rohrabacher said Mr. Chhun’s organization was far from clandestine. “We’ve all heard about them. We’ve all met with them. We’ve all talked to them. They are not a secret revolutionary cell,” the lawmaker said. “They’re outraged they cannot go back to their country and have an honest election.”

Mr. Rohrabacher said Mr. Hun Sen’s history demonstrates little allegiance to democracy. “Hun Sen is a former brigade commander of Pol Pot’s people, people who slaughtered millions of Cambodians,” the lawmaker said. “It’s a very good thing to resist tyrants and gangsters, and Hun Sen is certainly not a democratic leader.”

A spokeswoman for the Cambodian Embassy in Washington, D.C., did not return phone messages seeking comment for this article.

The indictment makes only one explicit allegation that Mr. Chhun’s group targeted civilians. The government alleges that in February 1999, Mr. Chhun ordered a grenade attack on a karaoke bar frequented by Vietnamese citizens. Several bar patrons were injured in the incident, according to the indictment.

A vice president of the Cambodian Freedom Fighters, Sokhom So, said yesterday that he was “very surprised” by Mr. Chhun’s arrest.

“He tried to promote democracy in Cambodia, American-style. Cambodia is still run by the Communists,” Mr. So said. Mr. So, who owns an Arlington, Va., jewelry store, said the arrest makes him question Mr. Bush’s commitment to encouraging democracy overseas. “That’s very, very disappointing for democracy lovers,” Mr. So said.

Asked about the delay between the alleged coup and the indictment, prosecutor Brian Hershman said, “It was a case that involved both international evidence and international witnesses. The time it takes can be longer in cases like that.”

Another factor in the timing could have been the statute of limitations. The indictment was returned five years to the day after Mr. Chhun allegedly traveled to Thailand to set up a base camp for the attempted coup. Most federal crimes have a five-year statute of limitations.

Mr. Chhun also cultivated ties with American political figures, especially Republicans. Since 2001, he has given at least $6,100 to the National Republican Congressional Committee.

A spokesman for the group, Carl Forti, denied Mr. Chhun’s claims in interviews that he was asked to work as a political fund-raiser in the Cambodian community.