More than a dozen police officers converged at a corner of Lafayette Square yesterday, bringing with them a horse and extra handcuffs.

Their target: a handful of demonstrators who had gathered to post two signs on an electrical box advertising a protest march Sept. 15 against the Iraq war.

During a clash that drew a crowd during lunchtime, two demonstrators, including an Iraq war veteran and the mother of another veteran, were arrested on charges of defacing public property. Police charged a third protester with impeding an officer.

"It was a case of extreme police overreaction," said Brian Becker, a protest organizer.

But Lt. Phil Beck of the U.S. Park Police said the officers took action only after the demonstrators ignored a command to remove a table and stop posting the signs.

The demonstrators, members of the antiwar Answer Coalition, have been in an ongoing dispute with the District and Park Service over their right to post signs in public places.

The D.C. government has fined the coalition about $20,000 for posting signs, and the Park Service has asked the group to remove them.

The coalition countered by filing a lawsuit challenging the District's regulations. The suit is pending.

The group assembled for a news conference yesterday at Lafayette Square to promise to put up more posters, regardless of possible sanctions. Within minutes, the pledge was tested. An officer approached and asked whether the demonstrators had a permit for their gathering.

As news cameramen focused in on the officer, he commanded the protesters to get back, ordered them to dismantle a table and called for backup.

The officer then got into a tussle over a bucket of paste with Tina Richards, the mother of an Iraq war veteran. "Let go of this," he shouted. "If you don't, you will be arrested."

More officers arrived, including several dressed in black commando-style uniforms and one atop a horse that he maneuvered to push back the crowd.

"Back up!" he shouted.

An officer placed handcuffs on Richards, of Missouri, and put her in the back of a police car. A few feet away, Kristine Klein, 13, Richards's daughter, started crying. She said that another officer had grabbed her arm and pushed her.

As Richards tried to call to her daughter from the cruiser, another officer closed the window.

When an officer went to speak to Kristine, a member of the Park Service's SWAT team advised him to stay away from her. "Don't feed into that, the cameras are rolling. Let her go," the officer said.

By then, officers had also handcuffed Adam Kokesh, a Iraq war veteran who lives in Washington and had been putting up one of the posters. Ian Thompson, 31, of Los Angeles was also arrested.

The arrested protesters were to be detained overnight before being charged today in D.C. Superior Court with misdemeanors, said Sgt. Robert Lachance, a park police spokesman.

After the officers took the protesters away, the crowd dispersed. The officers eventually left, but not before taking care of one last piece of business: removing the two signs.