COLUMBIA - Longtime political activist Brett Bursey violated federal law by disobeying a Secret Service agent's order to leave a spot within a few yards of where President Bush's limousine slowed to make a U-turn, a federal magistrate ruled Tuesday.

At the same time, U.S. Magistrate Bristow Marchant gave Bursey a sentence far less severe than the law allows and questioned whether federal prosecutors should have pursued the case. In a ruling from the bench, Marchant said Bursey meant no harm to the president, but rather was making what he believed to be a "principled stand" for freedom of speech.

Bursey was fined $500. The maximum penalty under the seldom-used law, which allows the Secret Service to temporarily restrict access to areas the president is visiting, is 30 days in jail and a $5,000 fine. Because the charge is a misdemeanor, Marchant heard the case without a jury.

Bursey, 55, who served a prison term for pouring blood over draft board records during the Vietnam War and who has been arrested several other times on protest-related charges since then, vowed to appeal.

"We may have lost this battle," Bursey said during a news conference outside the courthouse, "but we're winning the war ... by virtue of the fact that people who learned about this case thought it was outrageous."

He and his attorneys said they don't want to allow the current law to stand because it will set a precedent for chilling free speech.

Assistant U.S. Attorney John Barton, who prosecuted the case, said the guilty verdict means that "our office will continue to assist the Secret Service to protect the president. If a similar situation presents itself in the future, we will not hesitate to prosecute again."

The incident happened in October 2002 at Columbia Metropolitan Airport, where Bush spoke on behalf of Republican candidates for state office. Bursey had arrived with a sign reading "No War For Oil," a reference to the impending invasion of Iraq.

Bursey said he was told he had to go to a designated "free speech zone" a half-mile away. Bursey, the American Civil Liberties Union and others say such zones are a thinly veiled attempt by the Bush administration to force protesters to stay out of sight during presidential visits.

The ACLU has filed a civil lawsuit seeking a nationwide injunction barring the Secret Service from telling local police to shunt protesters into free-speech zones.

Marchant, in his ruling Tuesday, said that had Bursey been farther from where Bush's motorcade was to make its turn, he would have had had a stronger case that the Secret Service had acted unreasonably.

"In this age of suicide bombers," Marchant said, "the Secret Service's concern with allowing unscreened persons to stand in such close proximity to a slow-moving vehicle carrying the president is not just understandable, but manifestly reasonable."

Marchant rejected the prosecutors' argument, made in a written brief, that the courts shouldn't second-guess the Secret Service and law enforcement on security decisions.

"By bringing prosecutions under this statute, the government is ... drawing the courts into the debate over how far the government can go in restricting the rights of protesters and others in the exercise of their constitutional rights," Marchant said.

He said his rejection of arguments by Bursey's attorneys that the prosecutors violated Bursey's constitutional rights didn't mean that he agreed that they should have gone ahead with the case.

That, he said, "is a decision solely reserved for the government to make, and for the public to debate."