Threats against members of Congress who voted for the health-care overhaul have put law enforcement on alert around the nation and have led the Capitol Police and House officials to tighten security for lawmakers.

Capitol Police are providing threat assessments and security recommendations for House members' district offices and family homes, and are encouraging lawmakers and staff to report any harassment to them.

"The intensity of some of these threats is alarming," said Jamie Fleet, staff director of the House Commitee on Administration, which has jurisdiction over the Capitol Police, the agency responsible for protecting members of Congress. Rep. Bob Brady, a Philadelphia Democrat, is chairman of the committee.

Police are investigating "dozens" of incidents considered serious enough to warrant law enforcement attention, Fleet said in an interview.

At least four district offices of Democratic lawmakers were vandalized, in Arizona, Kansas, and New York. Ten members of Congress have disclosed threats against themselves or their families.

Since the House approved the health-care bill, 219-212, Sunday - with no GOP support - hateful rants against it poured in via voice mail, e-mail, and fax to the offices of Democratic lawmakers who voted for it. Yesterday, two Republicans said they, too, had been targeted as the parties squabbled over the increasingly heated rhetoric on health care.

House Speaker Nancy Pelosi (D., Calif.) said yesterday that it was "very important that across the board we all reject what has been said in the course of this debate, however it was provoked."

A threat to assault a member of Congress in retaliation for the performance of official duties is punishable by up to a year in prison.

A threatening note addressed to Democratic Rep. Kathy Dahlkemper of northwestern Pennsylvania arrived this week at the offices of the Armstrong County Commissioners. It called her a traitor and said, "You will never sleep through the night again."

Dahlkemper, of Erie, was among antiabortion Democrats who had hesitated to vote for the legislation because of concerns it did not do enough to prevent federal subsidies for abortions. She voted in favor after the group reached agreement with President Obama for an executive order affirming long-standing policy against public funding of abortion.

"Regrettably, my office has received a number of emails, letters, faxes and phone calls that are threatening or menacing in nature as a result of my vote in favor of health-care reform," Dahlkemper said in a statement yesterday.

"Most of these communications cannot be sourced; while some are coming from Western Pennsylvania, the majority of these inappropriate communications do not originate from my constituents," she said.

One e-mail addressed to Dahlkemper said: "Your names will be blotted from history and your offspring will suffer. It is written."

The note sent to the Armstrong County offices, where Dahlkemper holds constituent meetings twice a month, is being investigated by the county prosecutor and the FBI. No other communications have been referred to police, her office said.

Rep. Christopher Carney of northeastern Pennsylvania, another of the Democrats who voted for the overhaul after the abortion-policy agreement, has not received any particularly "outrageous" or threatening messages, his office said.

Rep. Bart Stupak (D., Mich.), who led the antiabortion holdouts, received a voice mail from a man who cursed him and said he hoped Stupak would die of rectal bleeding and cancer. A fax addressed to "Bart (SS) Stupak" had a picture of a gallows and a noose on it.

Some abortion opponents consider Stupak and his group of Democrats traitors to the cause because the opponents doubt the efficacy of Obama's executive order.

A spokeswoman for Rep. Patrick Murphy of Bucks County's Eighth District, who faces a strong challenge in his reelection fight, declined to comment. Murphy was one of many House Democrats who expressed concerns about the threats during a caucus meeting Wednesday night, Politico reported; the meeting was called by Brady and Capitol Police to discuss security.

"We're encouraging members and staff to be vigilant - that's really your best defense," Fleet said.

Republicans joined in the call for calm.

"When the government ignores the will of the people, a high level of frustration is to be expected," said Rep. Joseph R. Pitts (R., Pa.). "But that frustration needs to be channeled into political activity, not threats and violence."

Congress is about to begin its two-week spring recess, when lawmakers typically meet with their constituents.

"Other than the $1 million the DNC is spending on attack ads? The only threats have been of electoral retribution," said Kori Walter, spokesman for Rep. Jim Gerlach (R., Pa.). "All our windows are intact."