Anger over the health care overhaul has led to a nearly threefold increase in recent months in the number of serious threats against members of Congress, federal law enforcement officials said.

The lawmakers reported 42 threats in the first three months of this year, compared with 15 in last three months of 2009, said Senate Sergeant at Arms Terrance Gainer, who had information about threats involving both chambers.

"The incidents ranged from very vulgar to serious threats, including death threats," Gainer said. "The ability to carry them out is another question and part of an investigation to determine what, if any, appropriate steps to take."

Nearly all the recent threats appear to come from opponents of the health care overhaul, said Gainer, who also served four years as chief of the U.S. Capitol Police.

And, he said, there have been "significantly more" threats against House members than against senators.

The threats, which have led to at least three arrests, have not abated since President Barack Obama signed the measure into law March 23. The Capitol Police have contacted the FBI about such threats even more often since the law was signed, said Lindsay Godwin, an FBI spokeswoman.

House Speaker Nancy Pelosi, D-Calif., became the best-known of the recently targeted lawmakers Wednesday, when authorities accused a man in San Francisco of making dozens of threatening calls to her home and her husband's office.

In response to the threats, Capitol officials have been working to ensure that the 454 Senate offices across the country are secure. Some of the offices, a quarter of which are in federal buildings, are receiving additional equipment to help with the screening of mail.

A few members have reacted to the threats by lowering their public profiles.

Rep. Tim Ryan, D-Ohio, canceled an event at a Youngstown community health center because he received a threatening letter, his spokeswoman told a local television station.

And Rep. Betsy Markey, D-Colo., decided to hold conference calls with constituents, rather than in-person town halls, after getting threatening phone calls.