* Suspects wanted to commit holy war, police say

* NY Jews shocked to be target of purported attack

* Mayor, police commissioner greet worshipers

NEW YORK, May 21 (Reuters) - New York's mayor and police chief sought to calm Jewish worshipers on Thursday, the morning after authorities said they foiled a plot to blow up two synagogues and simultaneously shoot down military planes.

Four men arrested in the suspected plot were due to appear in court later in the day in White Plains, New York. Police Commissioner Raymond Kelly said all four had criminal records and did not appear to be part of al Qaeda.

As they greeted worshipers at one of the targeted synagogues Thursday morning, Kelly and Mayor Michael Bloomberg conveyed calm following the latest threat to New York City, which has been on high alert for another attack since the Sept. 11 hijacked plane attacks of 2001.

The FBI and New York police arrested the four Muslim men on Wednesday night after they planted what they believed to be explosives in two cars -- one parked outside each synagogue -- and planned to head to an air base with what they thought was an activated stinger surface-to-air missile.

But the explosives were inert and the stinger deactivated as the four suspects had been infiltrated by an FBI informant who provided the fake weapons.

"They stated that they wanted to commit jihad," Kelly told reporters, using a term that can mean holy war. "They were disturbed about what was happening in Afghanistan and Pakistan, that Muslims were being killed. They made the statement that if Jews were killed in this attack that would be all right."

Worshipers at the Riverdale Jewish Center, an orthodox synagogue that had an early morning service, were shocked.

"It's just unbelievable, unbelievable, that it's here in this community," said Rose Spindler, who said she was a Holocaust survivor. "They should let us live. How can they come here and do that to innocent people? We were very lucky."

David Winter, the executive director of the Riverdale Jewish Center, said the possibility of an attack was "always in the back of your mind."

"We were shocked. The shock and being floored is followed by relief," Winter said.

The other target, the Riverdale Temple, is a reform synagogue.

The suspects were due in court on the day U.S. President Barack Obama was to speak on national security and outline his strategy for closing the U.S. prison at Guantanamo Bay where terrorism suspects are being held. [ID:nN20544607]

HOME-GROWN

None of the four suspects had any known connection to al Qaeda, Kelly said. One of them was of Haitian descent and the other three American-born.

"It speaks to our concern about home-grown terrorism ... that in many ways is the most difficult to address," Kelly said.

The two synagogues are in a wealthy area of the Bronx, just north of Manhattan and near a highway that leads upstate toward New York's Air National Guard base at Stewart airport in Newburgh, where authorities said the men planned to shoot down planes with surface-to-air guided missiles.

The suspects were identified as James Cromitie, David Williams, Onta Williams and Laguerre Payen. Kelly called Cromitie, 53, the leader of the group. Two of the others were aged 29 and 33. Kelly said they may have converted to an extreme vision of Islam in jail, he said.

Each man is charged with one count of conspiracy to use weapons of mass destruction within the United States, which carries a maximum penalty of life in prison, and one count of conspiracy to acquire and use anti-aircraft missiles, which also carries a maximum penalty of life in prison.

All the men lived in Newburgh, about 60 miles (100 km) north of New York City, authorities said.

According to investigators, Cromitie said if he died a martyr, he would go to "paradise" and that he was interested in doing "something to America," the complaint said.

In October, Cromitie and the other men began a series of meetings at a house in Newburgh to plot their attacks and just last month they selected the synagogue and Jewish community center and conducted surveillance, it said.

The complaint said they bought an arsenal in May that included improvised explosive devices containing inert C-4 plastic explosives and a surface-to-air guided missile provided by the FBI that was not capable of being fired.

In November, according to the complaint, Cromitie said, "The best target (the World Trade Center) was hit already" and "I would like to get (destroy) a synagogue." (Additional reporting by Mark Egan; Writing by Daniel Trotta; Editing by Bill Trott)