Bricks have been hurled through Democrats’ windows, a propane line was cut at the home of a congressman’s brother and lawmakers who voted for a federal health care bill have received phone threats in the days before and after passage of the sweeping legislation.

Authorities are investigating incidents in Kansas, Virginia and other places, including Rochester, N.Y., where a brick tossed through the window of a county Democratic Party office had a note attached that said: ‘‘Extremism in defense of liberty is no vice,’’ roughly quoting the late Barry Goldwater, the 1964 Republican presidential nominee.

The FBI and Capitol Police were briefing Democratic lawmakers on how to handle perceived security threats after at least 10 reported incidents, said House Majority Leader Steny Hoyer, D-Md.

Those who feel they are at risk will be ‘‘getting attention from the proper authorities,’’ Hoyer said, declining to say whether any are now receiving added security. Normally only those in leadership positions have personal security guards.

The threats surprised an official with a think tank that monitors extremist groups.

‘‘I think it is astounding that we are seeing this wave of vigilantism,’’ said Mark Potok of the Alabama-based Southern Poverty Law Center.

In Virginia, authorities were investigating after someone cut a propane line leading to a grill at the Charlottesville home of U.S. Rep. Tom Perriello’s brother. Perriello also said a threatening letter was sent to his brother’s house.

The home’s address was posted online by tea party activists angry about the Virginia Democrat’s vote in favor of the health care overhaul. They had mistaken the brother’s address for that of the lawmaker.

Potok compared the online posting of a public official’s address to tactics used by hate groups.

‘‘This is what neo Nazi leaders in America do today,’’ Potok said. ‘‘They post personal information about their enemies and sit back and wait for somebody else to act.’’

In western New York, police are investigating after bricks were thrown through windows at two Democratic offices, but there have been no arrests. One was thrown through a window at Democratic Rep. Louise Slaughter’s district office in Niagara Falls early Friday.

Slaughter, whose district stretches from Rochester to the Buffalo area, has been a key supporter of the health care reform bill passed by the House on Sunday.

Sometime from late Saturday or Sunday in Rochester, N.Y., a brick was hurled at a wooden-framed glass door of the county Democratic Committee offices. The county party’s spokesman, Sean Hart, said the glass ‘‘only spider-webbed’’ but didn’t shatter, and the brick then appeared to have been picked up and thrown through the adjoining glass door.

Attached to the brick in Rochester was the note scribbled with the Goldwater quote.