W By Richard A. Serrano

ASHINGTON – Hate crimes and other acts of vengeance against Muslims and other immigrants from the Middle East skyrocketed nationwide after the Sept. 11 terrorist attacks, according to a long-awaited FBI report released Monday.

But Islamic leaders in Washington and elsewhere, many of whom were themselves the targets of outrage, said the new numbers fall short of the actual figures. Countless immigrants surely were afraid to report acts of retribution, they said.

The FBI found that while attacks against Muslims had previously been the least common hate crime against a religious group – just 28 in 2000 – the number of incidents surged to 481 in 2001.

The huge rise is “presumably as a result of the heinous incidents that occurred on Sept. 11,” the FBI said.

Ibrahim Hooper, spokesman for the Council on American-Islamic Relations, said that while much of the bias has tapered off, there was a tremendous backlash at first.

“These new numbers come from the initial weeks and months after 9/11, when it was just basically out of control,” he said. “We couldn’t keep up with the reports.”

According to the FBI report, most incidents targeting Muslims and others of Middle Eastern background involved assaults or intimidation. There were three cases of murder or manslaughter and 35 arson fires, the FBI said.

The hate-crime statistics were drawn from almost 12,000 local, state and federal law-enforcement agencies throughout the United States. Areas with large Muslim populations, such as Southern California, Chicago, Detroit and Washington, reported the most incidents. The report did not break down the increases in specific cities.

Much of the retaliation continued into the early part of this year, until the U.S.-led war in Afghanistan began to wind down.

Hooper and other Arab-American leaders said many immigrants stayed home in the days after Sept. 11, afraid to go to work or school for fear of retaliation. In many cities, mosques were the target of vandalism.

Many Muslims were afraid to report hate crimes to the FBI, out of fear the bureau would want to investigate them, Hooper and others said.

Mohamad Ali Elahi, the imam at the Islamic House of Wisdom in Detroit, where a half-million American Muslims live, said many people of the Islamic faith still suffer emotionally from the backlash.

“For us, the pain continues,” he said. “The prejudice that was produced after this disastrous event insulted the sacredness and the belief system of our faith community.”