SAN FRANCISCO -- Peace activist Cindy Sheehan announced Thursday that she will not run against Sen. Dianne Feinstein in the Democratic primary.

Sheehan, who camped outside President Bush's Texas ranch to protest the Iraq war that claimed her son's life, said she won't challenge the state's senior senator even though she thinks Feinstein hasn't done enough to oppose the war.

"I think I'm more effective on the outside than on the inside," Sheehan said during a news conference across from San Francisco City Hall.

Sheehan's comments echoed a suggestion made earlier this week by Sen. Barbara Boxer to a group of reporters.

"I don't think having her in the Senate election helps her at all," Boxer said. "I think it might have the opposite effect."

Sheehan, 48, was arrested last week before Bush's State of the Union address and ejected from the House of Representatives gallery on a charge of unlawful conduct for wearing a T-shirt with an anti-war message. Capitol Police later dropped the charge, but Sheehan said Thursday that she plans to sue over the incident.

During a trip to Venezuela last month, Sheehan said supporters had encouraged her to take on Feinstein in the June primary, but that she would have to consult with her family before entering the race.

Sheehan of Berkeley said she plans to pitch her tent outside the president's ranch in April.

Her son, Casey Sheehan, 24, was killed in Iraq in 2004.