WASHINGTON — Representative Pete Sessions, a Texas Republican, is no stranger to town hall meetings and their political possibilities. Four summers ago, he helped his party use them to stoke opposition to President Obama’s health care bill. Across the country, forums like his fed a budding Tea Party movement and set the stage for returning the House to Republican control in 2010.

But when Mr. Sessions returned to his Dallas-area district for the August recess this year, a pause before Congress takes up an agenda that includes immigration, government surveillance, health care and budget cuts, there was something conspicuously missing from his schedule: a town hall.

One of his constituents, Katrina Pierson, 37, who describes herself as a “conservative grass-roots volunteer” and had hoped to press Mr. Sessions on his commitment to pulling financing from the health care law, is so exasperated that she and a group of like-minded advocates have offered to host a meeting for him.

“He can just give us a date,” she said. “We’ll set it up.”

Though Republicans in recent years have harnessed the political power of these open mic, face-the-music sessions, people from both parties say they are noticing a decline in the number of meetings. They also say they are seeing Congressional offices go to greater lengths to conceal when and where the meetings take place.

“The whole thing is very anti-democratic, and it’s classic behavior of entrenched insiders,” said Matt Kibbe, the president of FreedomWorks, a Tea Party group that in 2009 helped send legions of demonstrators to town halls. Now, it is trying to draw out seemingly reluctant members by staging public events like mock meet-your-lawmaker meetings with empty chairs. “We’ve lost that Rockwell image of citizen participation in democracy.”

With memories of those angry protests still vivid, it seems that one of the unintended consequences of a movement that thrived on such open, often confrontational interactions with lawmakers is that there are fewer members of Congress now willing to face their constituents.

Members of Congress and their aides were reluctant to talk about the lack of town halls on the record, mindful of the pressure from liberal and conservative groups alike. “Ninety percent of the audience will be there interested in what you have to say,” one Senate Republican aide said. “It’s the other 5 or 10 percent who aren’t. They’re there to make a point and, frankly, to hijack the meeting.”

Indeed, many who attend the meetings now seem intent on replicating clashes like one in Pennsylvania in 2009, when Senator Arlen Specter, a Republican turned Democrat, was shouted down by an angry constituent, a scene captured on camera and played on an endless loop on cable news.

“The reason 2009 was so successful for the grass roots was because the politicians never saw it coming,” said Jennifer Stefano, the state director for the Pennsylvania chapter of Americans for Prosperity, a Tea Party group. “Now they know. And they are terrified.”

Many lawmakers, often from safe districts, are still holding town halls throughout the month. While a number of them are drawing voters outraged over Mr. Obama’s health care law, the intensity is nothing compared to the scale of 2009.

But where there are no gatherings, some groups have decided to take matters into their own hands.

After seeing a paltry schedule of Congressional town hall meetings this month, another major conservative group, Heritage Action for America, decided it would stage public forums of its own from Arkansas to Pennsylvania. The aim is to recruit people for a group it calls the Sentinels, a citizens’ brigade of sorts, to reach lawmakers through other means, like writing letters to the editor, dialing in to talk-radio programs and mastering the language of Twitter and Facebook.

The Democratic Congressional Campaign Committee is sending its advocates into Republican districts with two-dimensional cutouts of members without a traditional town hall on the calendar. Anyone who is feeling especially theatric is being encouraged to debate their cardboard congressman.

This month, the committee sent a batch of rubber ducks to Representative Rodney Davis, Republican of Illinois, who is under pressure to support a broad immigration overhaul. (The joke: He is “ducking” questions in an ethics investigation.)

Others on the Democrats’ target list have included Representative Tim Griffin of Arkansas, who was greeted at an airport by protesters calling for an end to the across-the-board budget cuts known as the sequester, and Representative John Kline of Minnesota, who is also being pressed to support immigration overhaul and was picketed after attending a closed-door Chamber of Commerce event. Not one of the Republican congressmen has a town hall scheduled this month.

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Brandon Thibodeaux for The New York Times

Political campaigners meeting in Dallas. Some town hall advocates have even offered to host one for Representative Pete Sessions.