DENVER -- Vice President Dick Cheney does not have to testify as an eyewitness in a civil lawsuit filed against Secret Service agents by a man who says he was wrongfully arrested for criticizing the vice president -- at least not yet, U.S. District Magistrate Judge Craig Shaffer ruled Tuesday.

The judge, who issued a written decision, left open the possibility that he may change his mind if Steven Howards can prove that Cheney has information that others can't provide about the 2006 encounter in the Colorado ski resort town of Beaver Creek.

Howards, a 55-year-old environmental consultant, said that he had approached Cheney while the vice president was on a walk in town and told him: "Your policies in Iraq are disgusting."

Howards said he also had lightly touched Cheney on the shoulder, then walked away. A Secret Service agent later caught up to Howards and arrested him on suspicion of assault.

Assault charges were never filed. Howards was issued a summons for misdemeanor harassment, but the Eagle County district attorney later dismissed the charge, saying it was clear that Howards hadn't attacked Cheney.

Howards later filed a federal lawsuit, claiming that the agents had violated his right to free speech and arrested him without probable cause -- possibly in retaliation for his critical comment.

Four Secret Service agents and two White House staffers who saw the encounter have since given conflicting views of what happened. Though he was listed as the victim, Cheney was not interviewed.

"The vice president is clearly a man who should know" what happened, Howards' attorney, David Lane, said at a March 11 hearing.

Cheney's lawyer, James Gilligan, argued that Howards had to prove Cheney had "unique personal knowledge" essential to the case in order to compel the testimony of such a high-ranking official. Ordering his testimony, Gilligan said, would be starting down a "slippery slope."

Lane said he would appeal Shaffer's decision.

"Frankly, Cheney should be volunteering to step forward and tell everyone what he knows," he said.

deedee.correll@latimes.com