"I was disappointed," Gainer said. "I know that holiday weekend everyone was prepared for less work, but it was disconcerting that an inordinate number did not come in."
U.S. Park Police officers also are weary from constantly working longer shifts under the heightened terrorism alerts, officers said.

Officers staff the barricades at Maryland Avenue and Second Street NE.
(Rich Lipski -- The Washington Post)
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Park Police officers, charged with protecting the nation's monuments on and around the Mall, or what they call the icons, also have worked 12-hour days. Park Police Officer Jim Austen said the officers are starting to get some relief in their schedules but are "burned out."
Each police chief is handling the heightened alerts differently. D.C. Police Chief Charles H. Ramsey put his officers on 12-hour shifts with no days off for several weeks right after Sept. 11, 2001. But he said recent intelligence briefings have not convinced him that he needs the longer shifts and reduced time off.
Ramsey said that if the intelligence becomes more specific and imminent, he won't hesitate to take the same steps as the Capitol Police.
"I'll go to 12 hours or longer than that in a heartbeat if I have to," Ramsey said. "We'll cancel days off or leave. We'll do whatever we have to. This is the new normal."
At the same time, Ramsey said, big-city police departments are struggling to strike a balance between responding to terrorism and protecting the public from other social ills.
"I deal with day-to-day crime in addition to terrorist threat," Ramsey said. "I've got to be able to do both."
With a constant barrage of new intelligence from the CIA and other sources, though, sustainability has become the watchword.
"This is a threat with no end in sight," Wexler said.
Staff writers Michael Powell and Michelle Garcia in New York and Mary Beth Sheridan in Washington contributed to this report.