His captors said it was time to "swim in cold weather," Basu Sigdel recalled.

Blindfolded and stripped to his undershorts, the 40-year-old lawyer struggled to breathe as strong-armed men repeatedly plunged his head into a water-filled steel drum, Sigdel said in an interview. They demanded to know the whereabouts of several Maoist rebels, accusing him of lying when he said he didn't know.

"It was so long that I almost choked, and I felt that I might die," Sigdel said, describing the early morning interrogation on the fourth day of his 50-day unofficial detention by Nepal's security forces last winter. "I could feel foam coming out of my mouth. Most probably the water got into my lungs."

Sigdel's ordeal highlights what human rights monitors call a pattern of abuses by government security forces, who have received roughly $22 million in U.S. military aid over the last several years. The forces are struggling to contain a Maoist insurgency that began in 1996 and recently has spread to virtually every corner of this picturesque Himalayan kingdom.

In a report last month, New York-based Human Rights Watch accused both the Maoist rebels and government forces of "summary executions, torture, arbitrary arrests and abductions, and persecution based on political associations." Of particular concern, the report said, was the growing phenomenon of "enforced disappearances," in which rebels or people suspected of helping them -- a loose category that includes lawyers who argued their cases in court -- were secretly taken into custody by the army or police and sometimes tortured or killed.

One disappearance that has received widespread attention involves a 15-year-old girl, Maina Sunuwar, who allegedly was murdered by soldiers in the Kavre district earlier this year. The incident occurred after the girl's mother claimed in statements to journalists and human rights workers to have witnessed an extrajudicial killing.

"There has been a massive increase in the number of disappearances" since the breakdown of a cease-fire agreement between the rebels and the government in August 2003, said Achyut Acharya of the National Human Rights Commission in Nepal, which has recorded 1,260 cases of disappearance involving security forces since 2000. "Most of the disappeared cases are in detention centers controlled by the army."

Brig. Gen. Dipak Gurung, chief spokesman for the Royal Nepal Army, said he would "not rule out the fact that some human rights violations might have taken place," and he acknowledged that the army sometimes held people without disclosing their whereabouts.

He said such methods were necessary to avoid compromising investigations and that torture and other forms of abuse were contrary to army policy. Gurung noted that in 2002, the army established a special "human rights cell" to investigate claims of abuses and had sometimes prosecuted soldiers accused of particular crimes.

Gurung also asserted that claims of abuses should be treated with skepticism because they often were based on information from "Maoists and Maoist sympathizers."

The army has no monopoly on mistreatment of civilians. According to human rights groups, the Maoists have grown increasingly brutal in their methods, which include cutting out the tongues of suspected informants and burning them alive.

Once part of Nepal's political mainstream, the Maoists took their movement underground in 1996 and launched what they call a "people's war" against the constitutional monarchy now run by King Gyanendra. His family has dominated this impoverished and isolated country of about 25 million people for more than two centuries. Nepal has not had a functioning parliament since 2002, and Gyanendra has assumed an increasingly autocratic role, political analysts say.

So far, human rights monitors say, about 10,000 people, many of them noncombatants, have died in the conflict.

Over the last two years, the Maoists have made steady gains and now roam freely throughout most of Nepal's 75 administrative districts, according to Western diplomats. Maoist attacks on police outposts have proved so effective that the government has closed roughly 80 percent of them.

The Maoists have also struck in the capital, Katmandu, staging several high-profile assassinations and, in September, a bomb attack against a cultural center affiliated with the U.S. Embassy. The bombing caused no casualties but helped precipitate the withdrawal of Peace Corps volunteers from the country.

U.S. officials contend that a Maoist takeover could be disastrous for the region, especially for India, an increasingly close ally that is battling several Maoist insurgencies of its own. The United States is supplying Nepal's army with M-16 rifles, night-vision gear and body armor and has dispatched Special Forces instructors to train troops in counterinsurgency tactics.

Human Rights Watch accused the United States of paying insufficient attention to complaints of abuses by the army. It said that the U.S. Embassy had not issued any statements critical of army actions, though it has routinely condemned Maoist atrocities.

In an interview, U.S. Ambassador James F. Moriarty described that statement as "flat-out wrong." But he added: "I do not think abuses are part of government policy. . . . We have seen individuals tried and convicted, court-martialed." The military aid is necessary, he said, for the simple reason that without it, the Maoists might win.

"You should never underrate the possibility of a Maoist takeover, particularly given the horrors that that would entail," he said.

Sigdel, the lawyer, seems an unlikely participant in the conflict.

A farmer's son with a wife and three children, he works out of a grubby second-floor walk-up with no computer, earning a modest living, he said, from land disputes, commercial cases and other routine civil matters. He described himself as apolitical, but once served on a human rights committee of the Nepal Bar Association. On several occasions, he has represented families trying to learn the whereabouts of relatives picked up by security forces on suspicion of involvement with the Maoists, he said.

On the morning of Jan. 22, Sigdel said, he was confronted in his office by three men in civilian clothes, who refused to identify themselves or produce an arrest warrant. He was bundled into a small van, blindfolded with dark goggles and a cloth sack and driven to what he presumed was an army facility in Katmandu.

For the next 50 days, he said, he was kept alone in a tent and repeatedly questioned about his political views as well as his purported associations with Maoists, of whom he claimed to have no knowledge. During the dunking session, he recalled, he struggled so violently for air that he opened wounds on both knees.

Shortly after his disappearance, Sigdel's wife, Sharda, filed a legal petition demanding that the army produce her husband in court, but the government denied knowledge of his whereabouts, Sigdel said. He was returned to his home one evening after signing a document falsely stating that he had been treated well, Sigdel said.

Gurung, the military spokesman, confirmed that Sigdel had been held in army custody. "I don't think he was that brutally handled -- maybe a bit roughed up," Gurung said. Asked specifically about the immersion treatment, a technique known to human rights workers as "submarining," Gurung acknowledged the possibility that it had occurred: "We don't have truth serum," he said. He added: "If it happened, he should lodge a protest."

Basu Sigdel, a 40-year-old lawyer, said he was abused by Nepalese forces during his 50-day detention last winter.