FBI agents have arrested a Pakistani American and his father in a California farming town after the son allegedly acknowledged that he attended an al Qaeda-run training camp in Pakistan and volunteered to carry out attacks on U.S. supermarkets and hospitals, officials said yesterday.

Two Muslim clerics from the area have also been detained on immigration charges in connection with the case. Federal and local terrorism investigators are trying to determine whether the four men are part of a broader network of al Qaeda supporters in the San Joaquin Valley, an agricultural area south of Sacramento, officials said.

If the allegations contained in court documents are accurate, the case provides a rare look at the unraveling of a potential terrorist plot on American soil. The case also illustrates the challenges posed by Pakistan, a key ally in the war on terrorism even as it continues to serve as a breeding ground for Islamic militants.

Hamid Hayat, 23, and his father, Umer Hayat, 45, an ice cream truck driver from Lodi, Calif., were arrested late Sunday and are being held on charges of making false statements to the FBI, officials said yesterday. Immigration officials said they had arrested two Lodi imams, Mohammed Adil Khan and Shabbir Ahmed.

Authorities said more charges and arrests are possible. "We believe through our investigation that various individuals connected to al Qaeda have been operating in the Lodi area in various capacities," Keith Slotter, who heads the FBI's Sacramento office, told reporters at a news conference. He acknowledged that there was no evidence Hayat had a specific attack plan.

Hamid Hayat came to the FBI's attention May 29 when he was returning from Pakistan on a flight from South Korea to San Francisco. Authorities discovered that his name appeared on the government's "no-fly list" but -- after the plane was diverted to Japan and Hayat was interviewed by the FBI -- he was allowed to continue to the United States.

In California, the FBI interviewed Hayat again, and he denied any connections to terrorists or training camps, according to an FBI affidavit unsealed late Tuesday night. But after a polygraph test indicated evidence of deception, according to the affidavit, Hayat acknowledged he spent six months in 2003 and 2004 at a Pakistan camp he said was "run by al Qaeda."

There he received training in weapons, explosives and hand-to-hand combat, according to information in the affidavit from FBI special agent Pedro Tenoch Aguilar.

The affidavit also says that Hayat "specifically requested to come to the United States to carry out his Jihadi mission. Potential targets for attack would include hospitals and large food stores."

Hayat's father also initially denied any connection to terrorism but -- after being confronted with a videotape of his son's account -- acknowledged he had toured several militant camps in Pakistan and that he had paid the airfare and expenses for his son's training at one of them, according to the affidavit.

He also identified the leader of the camp as a close family friend, Maulana Fazlur Rehman. Hayat apparently was referring to a man with a similar name who has been detained by Pakistani authorities on several occasions.

One surprising allegation in the affidavit is the reference to the previously unidentified al Qaeda camp, which Umer Hayat identified as "Tamal." Such a camp would be close to Rawalpindi -- home to Pakistan's military and intelligence service -- and to Islamabad, Pakistan's capital.

Officials cautioned that the FBI has not confirmed many aspects of the Hayats' accounts including details about the camp.

According to the affidavit, Hamid Hayat told the FBI that those at the camp were trained how to kill Americans. Hayat said he "observed hundreds of attendees from various parts of the world at this camp," and that they rotated in and out depending on their level of training, the affidavit said. They were given a choice of where to carry out attacks -- the United States, Afghanistan, Iraq, Kashmir and elsewhere.

Umer Hayat has run into trouble with federal authorities before: Customs and Border Protection officials seized $27,000 he did not declare as he prepared to board a flight in the United States several years ago, an agency official said. He was allowed to keep $1,000.

The Hayats live in a working-class neighborhood of Lodi, a city ringed by thousands of acres of vineyards and farmland in the Sacramento Delta. Their street, like their neighborhood, is made up largely of single-family houses and small apartment buildings.

Connie Fink lives next door to the complex of disheveled cottages where the Hayats have lived for at least five years, in an apartment she said is directly in front of their house. She said she considers the neighborhood somewhat unsafe but never dreamed anyone in the area would be accused of terrorism. "I guess you never really know who your neighbors are," she said.

The Hayats live five minutes from the Lodi Moslem Mosque, a yellow clapboard building across from a city park and the Lodi Boys and Girls Club. Shabbir Ahmed, one of the men arrested on immigration charges, serves as the mosque's imam. The other immigration defendant, Mohammed Adil Khan, is affiliated with the Farooqia Islamic Center outside town, officials said.

A string of men in robes and traditional Muslim caps filed into the Lodi mosque yesterday afternoon, but most declined to comment on the arrests. One man, Mohammed Pervaiz, said he did not know the Hayats but had seen them during prayer sessions.

"People who come here are peaceful," he said. "We come to pray. We are all human beings innocent until proven guilty in a court of law."

Nieves reported from Lodi, Calif. Staff writer Sara Kehaulani Goo and researcher Julie Tate in Washington contributed to this report.

Umer Hayat, left, and his son, Hamid Hayat, were arrested by the FBI after the son allegedly acknowledged he attended an al Qaeda camp in Pakistan.