TUCSON — Some U.S. Border Patrol agents along the Mexican border are packing paintball rifles, but they’re not being used for games.

Agents in the patrol’s Tucson, San Diego and Yuma sectors have been armed with guns that launch pepper spray and paintball projectiles and are trained to fire paintballs when they come under attack along border fences.

Splattering paint on rock throwers at high velocities is intended to dissuade them and to combat what has become a sharp increase in the number of rockings and other assaults on agents along the Mexican border.

“It has become a very effective tool,” said Border Patrol spokesman Ramon Rivera. “It has helped agents dramatically.”

The Border Patrol has about 1,000 of the paintball guns, which have been in the hands of agents since October. The gun, known as the FN303, is produced by a Belgian company and it replaced a less effective paintball gun that was used for three or four years in Nogales, Ariz., Rivera said.

At a range of about 225 to 250 feet, someone hit with a paintball could end up with stinging, welts, bruises or contusions, “and you’re not going to just be able to wipe it (the paint) off your clothes,” Border Patrol spokesman Lloyd Easterling said.

“It certainly lets you know that you’ve been hit with one of these things; it’s designed for you to take note and to stop what you’re doing.”

Jennifer Allen, director of the Border Action Network, a human rights organization based in Tucson, said she’s encouraged by the agency’s efforts.

“We have encouraged the Border Patrol to utilize nonlethal responses,” she said. “We’ve encouraged training for agents that has them better prepared to de-escalate rather than escalate situations, and to respond with appropriate level of threat.”

“We are encouraged by the Border Patrol’s following through and looking into implementing nonlethal strategies. However, I think we’re going to see the level of violence continue to escalate on the border until we have comprehensive immigration reform,” Allen said.

Assaults on agents frequently occur as groups of illegal immigrants stage along border fences, waiting for an opportunity to cross into the United States, or soon after they’ve already done so.

The number of rockings, and of total assaults on agents — including attacks involving vehicles, Molotov cocktails and firearms — have jumped sharply along the Mexican border.

From Oct. 1 through March 31, there were 577 assaults on agents, compared to 426 assaults reported borderwide over the same period a year earlier; rockings increased to 424 from 273 over the same comparable dates.

Agents in the San Diego sector have experienced 217 rockings in the 2008 fiscal year that began in October, followed by 132 in the Tucson sector, which covers most of the Arizona-Mexico border.

Easterling said the launcher gives the Border Patrol agents a way to deliver projectiles, either an irritating pepper agent or paint to mark a target, so they can counter aggressive behavior.

“They’re designed to stop the threat, basically, and incapacitate a target without causing any critical injuries,” he said.

Rivera said the paintball launchers have been fired on 21 occasions.

Each agent in those incidents could have fired several magazines full of rounds, Rivera said. The 29-inch-long rifle, with a compressed air canister that fires the 15 projectiles in its magazine, resembles a Vietnam-era grenade launcher but weighs only about 5 pounds.

Most of the time, he said, “we do what’s called saturation: shoot the pepper pellets around a group of rock throwers to get them to stop throwing rocks that can end up hurting or possibly killing an agent.”