By DAVID M. HERSZENHORN and SHERYL GAY STOLBERG
WASHINGTON — Senator Arlen Specter and the health and human services secretary, Kathleen Sebelius, were heckled and booed in Philadelphia on Sunday.
In Austin on Saturday, a throng of protesters enveloped RepresentativeLloyd Doggett, Democrat of Texas, at a supermarket where he was trying to meet constituents. They carried signs that said “No Socialized Health Care” and chanted “Just say no!”
And in Morrisville, Pa., Representative Patrick J. Murphy, a Democrat, expected 25 people at a “Congressman on Your Corner” event on Saturday. Instead he was met by a boisterous crowd of about 150 and a barrage of questions on health care.
The protests, organized by loose-knit coalition of conservative voters and advocacy groups, were a raucous start to what is expected to be weeks of political and ideological clashes over the health care overhaul President Obama is trying to push through Congress.
The conservative groups, including FreedomWorks and Americans for Prosperity, are harnessing social networking Web sites to organize their supporters in much the same way Mr. Obama did during his election campaign. Democrats said they expected supporters of the health care overhaul to mobilize against Republican events later in the month.
Republicans, however, seemed to get the early jump, in part because Democrats, who hold the majority in Congress, have scheduled numerous events, including forums and town-hall-style meetings, to discuss the proposed health care legislation with constituents.
The Texas protest against Mr. Doggett was coordinated by Heather Liggett, who has worked with the local Republican Party, as well as the state chapter of Americans for Prosperity, to organize antitax “tea party” demonstrations.
When a member of her group saw a newspaper advertisement about Mr. Doggett’s event, Mrs. Liggett posted it on her Web site, she said, and the word spread “like a domino effect” through her network. She estimated that 450 people showed up.
Mrs. Liggett said she was also in touch with conservative voters around the country who were helping organize similar events. “Whether it’s Arlen Specter or Claire McCaskill or Lloyd Doggett, they are showing up in force,” she said, referring to the Democratic senator from Missouri.
Mr. Doggett said he had been ambushed while trying to hold “neighborhood office hours” at a Randalls grocery store, where he usually gets questions about veterans’ benefits or listens to constituents’ advice on how to fix the budget deficit.
“If you look at the YouTube video, you can barely see in the edge of that a beautiful marble tombstone with my name on it,” he said. “People that worked so hard to get their signs in full-color did not come to dialogue. They came to be destructive.” Video of protesters confronting Mr. Specter and Ms. Sebelius in Philadelphia was also quickly posted to YouTube.
Mr. Doggett said: “This is not a grass-roots effort. This is a very coordinated effort where the local Republican Party, the local conservative meet-up groups sent people to my event.”
Some protesters blocked his car, then followed him to another event.
The effort to flood events held by Democratic lawmakers appears to be part of a concerted strategy that began earlier in the spring at the behest of conservative, libertarian and antitax groups.
One group, called Right Principles, which sent protesters to an event in May held by Representative Jim Himes, a freshman Democrat from Connecticut, has distributed a memorandum laying out strategies to “pack the hall” and pummel lawmakers with questions.
In Virginia, Bill Wilson, the president of Americans for Limited Government, a conservative group, issued a clarion call on Monday for protests against Representative Tom Periello, another freshman Democrat. Mr. Wilson urged residents of Mr. Periello’s district to “hold rallies, demonstrations, tea parties and protests in opposition to Barack Obama’s insidious efforts to take over the health system.”
Democrats have made plans for their own offensive, including a swing through Western states by Mr. Obama. They have accused Republicans of stifling discourse. “Conservative activists don’t want to have a conversation,” said Jennifer Crider, a spokeswoman for the Democratic Congressional Campaign Committee. “They want to disrupt.”
Republicans said that the protests were just the beginning of spontaneous opposition to the health care proposals and that they would only gain momentum as Americans learn more about the legislation. “The more the American people hear about the Democrats’ plan, the less they like it,” said Michael Steel, a spokesman for the House Republican leader, Representative John A. Boehner of Ohio.
In Washington, Amy Menefee, a spokeswoman for Americans for Prosperity, said her group was encouraging members to attend town-hall-style meetings and ask questions, including whether the lawmaker has read the entire health care bill. Ms. Menefee said her group was encouraging its members to “be respectful.”
FreedomWorks is doing much the same; it maintains a map on its Web site where members can post events in their communities.
In Texas, Shirley Markley of Austin said she received an e-mail message from a friend about Mr. Doggett’s meeting on health care and immediately wanted to attend. Once a liberal Democrat, Ms. Markley said, she voted for Senator John McCain for president last year and worries that Mr. Obama’s overhaul will lead to socialized medicine.
When she arrived at the store, she said, a large crowd had already surrounded Mr. Doggett. “People were shouting and booing his answers,” she said. “He said, ‘A few angry people won’t change my mind.’ ”
Eventually, Mr. Doggett cut the meeting short and headed for his car. “He jumped in and fled,” Ms. Markley said with a laugh. “It was like he was tarred and feathered and ridden out of town on a rail. It was a beautiful thing.”
Mr. Doggett said that he had tried his best to answer questions, but that the demonstrators expressed opposition not only to the health care plan but also to all government programs, including Medicare and Social Security.
He said that because of the protesters he was unable to speak to other constituents, including a father and his son, wearing a Boy Scout uniform, who wanted to talk about applying to one of the military academies. He said he remained firmly committed to the health plan.
“In Texas, not only with the weather but with the politics, it is pretty hardball around here,” he said. “I have a pretty thick skin about all of this. But this really goes over the line.”
Dan Frosch contributed reporting from Denver.