As a phalanx of motorcycles sped by on Old Philadelphia Pike in Lancaster County, Pa., in July, Tristan Egolf and six compatriots stripped to their skivvies and piled on top of one another in a pyramid, mimicking the infamous photograph taken at Iraq's Abu Ghraib prison.

But a minute after their bit of street theater had begun -- and long before a motorcade carrying President Bush had arrived -- police moved in and arrested six of the protesters on disorderly-conduct charges. The seventh man got away.

This month, Lancaster County's Republican district attorney dropped charges against the "Smoketown Six" -- named for the Amish country town that hosted Bush that day -- declaring that their "symbolic conduct" was protected by the First Amendment.

"They denied us our chance at expression," said Egolf, 32, a twice-published novelist who lives in East Lampeter Township, Pa. "That seems to be what they're doing these days: They don't agree with your opinion, so they haul you off and drop the charges later."

As Bush has traveled the United States during this political campaign, the Secret Service and local police have often handled public protest by quickly arresting or removing demonstrators, free-speech advocates say. In addition, access to Bush's events has been unusually tightly controlled and people who do not support Bush's reelection have been removed.

Although it's impossible to precisely measure the tactics in comparison with previous campaigns, civil liberties advocates and other experts say the treatment of dissenters is harsher this year. Several dozen protest-related arrests have been reported in recent months, in addition to the 1,800 made outside the Republican National Convention in New York, and the American Civil Liberties Union says that scores of other people have been evicted or denied entry to Bush campaign events.

"Every president wants to suppress speech at one point or another," said Christopher Hansen, an ACLU lawyer who tracks arrests and removals. "That said, the incidents seem to be more numerous this time around."

Alex Vitale, a sociology professor at Brooklyn College who studies police behavior at political protests, argues that the United States has not seen such tactics during protests since the Vietnam War era.

"This seems to be on a new level from what we've seen from past administrations," Vitale said. "It's clear that some of these security zones are not based on legitimate security concerns. They are based on the idea of the president not seeing someone who disagrees with him, which basically undermines the whole idea of the First Amendment."

Tickets to Bush events, distributed by the Republican Party, go only to those who volunteer or donate to the party or, in some cases, sign an endorsement of the GOP ticket and provide names and addresses. Party workers police the crowds for signs of Kerry supporters, who are frequently evicted.

Bush campaign spokesman Scott Stanzel said the tickets are distributed by precinct leaders and volunteers, who have discretion about who should receive them. He said those in attendance include undecided voters.

"We give out tickets . . . to people who support his reelection and people who may be undecided but want an opportunity to hear what he has to say," Stanzel said.

The Kerry campaign says it does not limit attendance based on political views, a point Kerry has made frequently when confronted by hecklers on the campaign trail. "We don't base entry to our events on political affiliation," said Kerry spokesman Phil Singer.

Critics also have raised questions about the role of the Secret Service, which has cordoned off broad areas around campaign events in the name of security and has, according to some complainants, played a role in arresting or removing law-abiding protesters.

A spokesman said that the Secret Service strives to stay out of any confrontations or disputes that do not involve a security threat and that the agency is often wrongly identified as being involved in arrests.

"As long as there's no security threat, the responsibility for removing someone from the site is the responsibility of the site's sponsor," said spokesman Tom Mazur.

During the Republican convention, more than 1,800 people were arrested by the New York Police Department; nearly all still face charges. There were only six arrests at the Democratic National Convention in Boston, but protesters complained that they were herded behind barbed-wire fencing far from the convention site.

Outside the conventions, a series of arrests have kept law enforcement officials busy during the campaign season. In September, the mother of a soldier killed in Iraq was arrested at a rally for first lady Laura Bush in Hamilton Township, N.J.; she was wearing a T-shirt that said "President Bush you killed my son." The charges were later dropped.

In another well-publicized case in July, Jeff and Nicole Rank were arrested and jailed on trespassing charges in Charleston, W.Va., for wearing shirts with anti-Bush slogans during an appearance by the president. The charges were later dropped, and the Ranks received apologies from local authorities, who said the arrests were made at the behest of the Secret Service.

The couple has filed a lawsuit against the Secret Service and a White House official. Mazur declined to comment on the case.

As for Egolf, he and his friends were not dissuaded by their summertime arrests. The group managed to get into a Bush rally yesterday in Lancaster, before being escorted out after they began heckling, Egolf said. The group then reenacted its Abu Ghraib pyramid in a designated protest zone nearby. This time, there were no arrests.

"At least I got to express my feelings," Egolf said, "even though we were quickly silenced."

Staff writers Dana Milbank and Jim VandeHei and research editor Lucy Shackelford contributed to this report.