“Our people in the neighborhood have been closely watching your activities and figured out you are a close associate of a secret Taliban movement on the U.S. Soil,” said the typewritten letter. “We ask you to leave the country as soon as possible otherwise one of our people is going to shoot you dead.”

National advocates for Sikh-Americans, known for aggressively defending their members against discrimination, sprang into action. They posted the letter on the Web site of the Sikh-American Defense and Education Fund, contacted law enforcement agencies and urged the victims to speak out.

The family was so unnerved by the letter that they asked the media not to reveal their names or faces. But Sikh-American leaders and residents in Sterling said the death threat was a rare, if chilling, exception in a region where their religious community - the fifth largest in the world - has established comfortable suburban roots.

“I can understand that people were upset after 9/11, but most people here are educated and open to us,” said D.J. Singh, 62, an accountant from Ashburn, wearing a business suit and a purple turban. “If people mistake us for Muslims, we need to educate them better about who we are, but we must also respect all religions.”

Last week, Loudoun County Sheriff Mike Chapman visited the gurdwara in Sterling - a Sikh place of worship - to reassure Sikhs that his force was working to protect them. Located in a nondescript industrial park, the gurdwara's doors opened to a serene sanctuary. Musicians sang hymns accompanied by tabla drums and harmonium, while women prepared a lunch of rice and lentil stew.

Chapman and 10 armed deputies tied on bright orange kerchiefs to cover their heads - all who enter a gurdwara must have their heads covered, as a show of respect to the Sikh scripture which is central to the gurdwara. They spoke of the Sikh-Americans as “model citizens,” greeted their leaders familiarly and sat cross-legged for the worship service and lunch.

Afterward, Chapman said his office and FBI investigators were working hard to “get to the bottom” of the threat.

The message brought some comfort to the software consultant, who had relocated in 2006 after experiencing similar threats while living in Gaithersburg and Leesburg. Once, he said, someone had chalked “Osama go home” on his driveway. Another time, he’d received a letter titled “Death death death.” Until last month, he thought he had escaped the hostility.

“Everyone here has been so nice and welcoming. I was comfortable before the letter, but now I am concerned,” said the man, who wore a brown turban. He said he had no idea who had sent the warning. “I am trying to maintain the Sikh spirit of always being positive. But I just want my family to be safe,” he said.