The arrests followed a generally low key anti-war protest marking the war's third anniversary. To the beat of a muffled drum and a ceremonial peace bell, about 200 people marched from the Lincoln Memorial across the Potomac River to the Defense Department headquarters in Arlington, Va.

Demonstrators chanted, "Peace now," as dozens among them crossed the fence and were taken into custody. Pentagon spokeswoman Cheryl Irwin said the 51 arrested were given misdemeanor citations that require their appearance at a federal court, and then they were released.

Among the protesters -- but not the fence climbers -- was Cindy Sheehan, who last summer staged a month-long protest outside President Bush's Texas ranch.