A New York City police officer was stripped of his gun and badge on Monday after an amateur video surfaced on the Internet showing him pushing a bicyclist to the ground in Times Square during a group ride on Friday evening.

The cyclist, identified in court papers as Christopher Long, 29, was taking part in a monthly ride, called Critical Mass, that often draws hundreds of riders. In a criminal complaint against Mr. Long, the officer, identified in the court documents as Patrick Pogan of the Midtown South precinct, says that the cyclist rode straight into him. But the video, posted on YouTube and on the blog Gothamist.com, shows the officer lunging toward Mr. Long.

The police said the officer had been assigned to desk duty pending a Police Department investigation. The police did not give the officer’s name or age or say how long he had been with the department.

The monthly rides have been a source of tension for the police since shortly before the Republican National Convention in 2004, when a large number of officers arrested more than 250 riders on charges that included parading without a permit.

In 2006, a state judge turned down a request by the city to forbid an environmental group that promotes the monthly rides from taking part in them, from gathering at Union Square Park beforehand and from mentioning the rides on its Web site.

According to members of the group, Time’s Up, the video was taken by a tourist standing on the sidewalk. It shows bicycles streaming down Seventh Avenue at 46th Street, past two uniformed officers standing in the middle of the avenue. After a few seconds, one of the two walks quickly toward the east side of the avenue and into the original path of Mr. Long’s bicycle. Mr. Long appears to try to steer clear of the officer, but the officer then shoves him. Mr. Long crashes onto the curb, and people gather around him and the officer.

Officer Pogan arrested Mr. Long on charges of attempted assault, disorderly conduct and resisting arrest, the court papers say. Mr. Long, who other cyclists said works in the Greenmarket in Union Square, was released without bail on Saturday.

In papers filed in Manhattan Criminal Court, Officer Pogan said Mr. Long was weaving in traffic, “forcing multiple vehicles to stop abruptly or change their direction” to avoid a collision. Officer Pogan also said he suffered cuts on his forearms as he fell to the ground.

Officer Pogan said Mr. Long had flailed his arms, kicked his legs and refused to put his hands behind his back. He also said Mr. Long had “twisted away” from him, “thereby making handcuffing difficult.”

He said Mr. Long told him: “You are pawns in the game. I’m going to have your job.”

The video clip ends soon after Mr. Long hit the ground. Witnesses challenged Officer Pogan’s account of the incident.

One cyclist, Craig Radhuber, 54, said he was a few feet behind Mr. Long, whom he said he did not know. He said Officer Pogan “body-slammed this kid off the bicycle so hard that he went from the lane to the curb.”

“I went over to yell at the police when another officer came and asked me to move back,” Mr. Radhuber said.

Mr. Radhuber said Mr. Long had not been weaving in traffic, as Officer Pogan alleged. “There was no traffic behind us — there was no traffic to weave in and out of,” Mr. Radhuber said. “The police officer looked to see who he was going to pick off.”

Bill DiPaola, a director of Time’s Up, said he arrived just after Mr. Long went down. “He got up and was dazed,” he said, referring to Mr. Long. Then, referring to Officer Pogan and the other officer in the video, he said, “They put their knees on top of his head and were smashing him into a phone booth.”

A lawyer for Mr. Long, Mark Taylor, said the cyclist had been “assaulted by the police.” He said Mr. Long, who was bruised but not hospitalized, was not available for interviews. “We believe the video speaks for itself,” he said, adding that he hoped the Manhattan district attorney’s office would drop the charges against Mr. Long.

Norman Siegel, a civil rights lawyer who represented Time’s Up in 2006, said he had been asked by its leaders to look at the video. He said it “shows unacceptable illegal behavior by this particular police officer.”

“Unfortunately, it’s another example of how the N.Y.P.D. has targeted without justification the Critical Mass bike riders,” he said.