On the U.S. West Coast, community leaders and law enforcement officials have issued a plea for tolerance in the wake of scattered incidents against Muslim Americans. They also issued a warning to those who take out their aggression on innocent people.

In a strong show of support for the local Muslim community, law enforcement officers and state and local officials joined religious leaders at a Los Angeles mosque.

Maher Hathout, a spokesman for the Islamic Center of Southern California, supported the call to action made by President Bush in the wake of last week's terrorist attacks. The Islamic center official also issued a plea to his fellow citizens. He said, "As the President said, we are at war. We will win this war, God willing. We will win it together, not divided. We will win it by not losing our values and what we hold dearly, and our liberty and the dignity of our citizens."

Around the United States, there have been threats and cases of violence against Arab-Americans and Muslims. Federal authorities are investigating some 50 incidents as possible hate crimes.

Hateful speech is not in itself illegal, says California Attorney General Bill Lockyer. But when coupled with a threat or an act of violence, it constitutes a hate crime. He says that even children have been victims. Mr. Lockyer said, "When five-year-olds in kindergarten get threatened, called names, called terrorists and sent home crying because of their ethnic or religious background or national origin, that kind of hate is not to be tolerated in this great state."

Federal authorities also say they are aggressively investigating all reports of hate crimes, including several murders. An Egyptian-American shopkeeper in Los Angeles was buried Wednesday. He was shot and killed Saturday in a crime that local officials believe was a botched robbery. The man was a Coptic Christian but his family believes he was targeted because he was mistakenly thought to be a Muslim. Federal officials now say they are investigating that crime.

In Mesa, Arizona, an Indian Sikh immigrant was also killed Saturday in a case that officials say was clearly a hate crime.

Los Angeles Sikh leader Opjit Ghuman says there have been many less-serious incidents in his own community, where Sikhs are sometimes mistakenly thought to be Muslim. "Our community people," he said, "often have grocery stores, little corner groceries, or are taxi drivers or are in the public going about their business and are subject to harassment."

Authorities say they take all reports of hate crimes seriously. Ron Iden is agent in charge of the Los Angeles office of the Federal Bureau of Investigation. "We want to be very clear," he said. "Threats and acts of violence against Muslim Americans or those thought to be Muslim Americans will not be tolerated. We will aggressively investigate violations of federal hate-crime law and we will bring those who violate those laws to justice."

Perpetrators of hate crimes can also be prosecuted in California under state and local statutes. California officials are distributing pamphlets in a range of languages, including Arabic, Farsi, Hindi and Vietnamese. The pamphlets urge members of ethnic communities to report hate crimes to local authorities.

At the Islamic Center of Southern California, spokesman Maher Hathout, flanked by state and local officials and other community members, said he appreciates the support for Muslim Americans voiced by President Bush, by law enforcement officials and other citizens. He also had a warning. "There are two dangers we ought to be vigilant and be very aware of," he said. "The problem will always be the fanatically ignorant and the wicked opportunist. And we should not allow either one of those to set a wedge or to divide America at a time when America is united."

Another Muslim community leader, Salam Al-Marayati of the Muslim Public Affairs Council, added "we are united against terrorism. We are united against hate."