FBI probes threats over Democrats' healthcare vote

* Senior House Democrat decries “very serious incidents”

* Palin tells supporters, “Don’t Retreat, Instead -- RELOAD”

WASHINGTON, March 24 (Reuters) - The FBI and police are investigating attacks and threats against Democratic members of Congress who voted for healthcare reform, and a senior House of Representatives Democrat said on Wednesday his colleagues are at risk.

Democrats decried heated Republican rhetoric, including 2008 vice presidential nominee Sarah Palin’s Twitter comment urging supporters, “Don’t Retreat, Instead -- RELOAD.”

A Palin Facebook post continued the firearms theme, featuring a U.S. map targeting 20 members of Congress who backed the healthcare legislation, using the crosshairs of a gunsight to note each of their home states.

The House gave the healthcare measure -- President Barack Obama’s top domestic priority -- final congressional approval on Sunday. Obama signed it into law on Tuesday. Emotions ran high among opponents and supporters during the yearlong debate over the legislation.

An FBI spokeswoman said the agency, the U.S. Capitol Police and other law enforcement officers are investigating threats and incidents of violence against members of Congress.

House Majority Leader Steny Hoyer said police and the FBI are concerned about “very serious incidents” that took place since Sunday’s vote.

Some lawmakers have received death threats, bricks were tossed through the windows of one House member’s office in New York state, another lawmaker was spat upon by a protester on Capitol Hill and another was the target of a racial slur.

In response to a reporter’s question, Hoyer said he considered his congressional colleagues to be at risk.

Representative Louise Slaughter, a New York Democrat whose Niagara Falls office was vandalized and whose campaign office received a voicemail referring to snipers last week, said in a statement she was disturbed that Republican leaders appeared to be “fanning the flames with coded rhetoric.”

Slaughter noted that Michael Steele, chairman of the Republican National Committee, took aim at House Speaker Nancy Pelosi in an interview on Fox News, telling viewers, “let’s start getting Nancy ready for the firing line in November.”

The Republican Party’s website features a picture of Pelosi in front of a wall of flames and urges visitors to the site to “make a donation to help us win 40 seats in 2010 and fire Nancy Pelosi.”

House Republican Leader John Boehner, also on Fox News, said, “There are a lot of angry Americans and they are angry over this healthcare bill. They’re angry about the fact that the Democrats here in Washington aren’t listening to them.”

But Boehner, who delivered an impassioned “Hell, no!” speech opposing the healthcare bill on the House floor, said that “violence and threats are not acceptable.” Instead, he said, Americans should register people to vote or volunteer for a political campaign. (Additional reporting by Jeremy Pelofsky and John Whitesides; editing by Will Dunham)