Frightened by a wave of violence and harassment, Sikhs across the country are struggling to explain to an uncomprehending public that despite their turbans and beards, they are not followers of the Taliban and not in any way responsible for last week's terror attacks. 

Although there are fewer than a half million Sikhs in the United States, they have attracted a disproportionate share of the anger following Tuesday's attacks. On Saturday in Mesa, Ariz., a gunman drove into a Chevron station and shot to death the Sikh owner. The gunman then fired on a Lebanese clerk at a nearby Mobil station and into the home of an Afghan family. 

''I'm a patriot,'' the suspect, Frank S. Roque, said as he was arrested. ''I'm a damn American all the way.'' 

Since the attacks, people who look Middle Eastern and South Asian, whatever their religion or nation of origin, have been singled out for harassment, threats and assaults. Mosques have been fired upon. Arab-owned businesses have been burned. A young Indian Catholic and his friend were beaten. 

The F.B.I. is also investigating two other shooting deaths as possible hate crimes. In San Gabriel, Calif., Adel Karas, an Egyptian Christian grocer, was killed Saturday at the market he owned. The same day, Waqar Hasan, a Pakistani Muslim, was found shot dead at his store in the Pleasant Grove section of Dallas. 

But the nation's Sikhs, conspicuous in turbans that resemble the head wrap of suspected terrorist Osama bin Laden, have suddenly found themselves particularly vulnerable. By yesterday afternoon, more than 200 Sikhs had reported incidents to a Sikh anti-defamation group. Newspapers around the country have reported that Sikh temples in Cleveland and West Sacramento were vandalized and, in San Mateo, Calif., a gasoline bomb was thrown through the window of a Sikh family's home, hitting a 3-year-old on the head, but not exploding. 

On Sunday, near Eugene, Ore., a 54-year old California woman was arrested for trying to pull the turban off the head of a Sikh man at a highway rest stop. 

''People in our community are just terrified,'' said Mandeep Dhillon Singh, a lawyer in Menlo Park who is a spokesman for the Sikh Media Watch and Resource Task Force. ''We haven't gotten beyond the shock of our own nation being attacked, and now we're being attacked.'' 

On Sunday, in a telephone conversation with President Bush, Prime Minister Atal Behari Vajpayee of India expressed concern about the safety of Sikhs in the United States. 

For many Sikhs, fear has disrupted the rhythms of daily life. ''I haven't been out much this week,'' said a Sikh woman in Atlanta, who spoke only on the condition she not be identified. ''It's a time to be very cautious. It's not a time to do any unnecessary shopping.'' 

Sikhism, founded in the late 15th century by Hindu-born Guru Nanak, is a monotheistic religion that has grown to become the world's fifth largest after Christianity, Islam, Hinduism and Buddhism. Sikhs reject the caste system, and to this day Sikh men take the name ''Singh'' and women, the name ''Kaur,'' to connote the equality of all believers. 

A majority of the world's 18 million or so Sikhs live in the Punjab region of northern India, but there are sizable Sikh populations in England, Canada and the United States. 

In the wake of the terrorism attacks, some Muslim and Hindus have discussed changing their traditional dress so as not to be conspicuous. But Sikh men say their religion requires them to leave their hair uncut and covered, either by a turban or a small bun called a patka. 

Balbir Singh Sodhi came to Mesa to open a gas station. Prosecutors said the only reason for the killing was his turban and his dark skin. At the time of the incident, he was outside the station doing landscaping with four Mexicans, but he was the only one shot. 

Lakhwinder Singh, a brother of the victim, said Sikhs in the Mesa area began hearing threats the day of the terror attacks. 

''My brother and I and some other Sikhs who owned stores talked about going to the media to try to clarify that we are not Muslims,'' said Lakhwinder Singh. ''We knew there was very little understanding of Sikhs in this country.'' 

Among Sikhs in the United States, there is now intense debate about how to go about distinguishing themselves from Muslims while not implying that attacks on Muslims are justified. 

''It would be antithetical to our faith to have materials saying, 'We are not Muslims,'' said Inderpreet Singh, a Sikh in Boston. ''It's understandable that people now are worried about being mistaken for Muslims, but we have to be very careful not to do that.'' 

In Chicago, Inderjit Singh, a Sikh taxi driver, yesterday taped a flier about his religion to the partition separating him from the passengers. 

The flier describes the history and basic beliefs of Sikhism, and then adds, ''Some people have the misconception that Sikhism is an offshoot of Hinduism or the Muslim religion when actually it is a separate religion by itself.'' 

Attackers, however, are making no such distinctions. In San Francisco, Sean Fernandes, a 26-year old Indian Catholic, said he was walking with a white Australian friend early Saturday morning, when a man came up, called him a ''dirty Arab,'' and punched him and the friend. His friend was stabbed in the ensuing brawl and remains hospitalized in critical condition. 

''I've lived in this country for eight years, and felt at home here, but this makes me re-evaluate,'' said Mr. Fernandes, a software engineer. ''I'm completely shocked. I've always thought people here were very tolerant, but I guess tough times bring out their true colors.'' 

Photo: Surinder Singh, a Sikh American, yesterday at the interfaith Day of Remembrance in San Francisco. (John G. Mabanglo/Agence France-Presse)(pg. B10)