All Washington public schools were closed Monday, Mayor Vincent Gray announced. The district readied for the storm's effects, which could include heavy rain, street flooding, strong winds, power outages and storm-surge flooding along the Potomac River and its tributaries, Gray said.
All federal buildings were closed to the public Monday and will be Tuesday as well.
President Barack Obama declared a state of emergency in the District of Columbia on Sunday.
The Maine Emergency Management Agency warned Sandy could create "significant problems" such as high surf, fierce winds and coastal erosion.
Flooding is also possible in areas where rain is heaviest, emergency officials said.
In anticipation of widespread power outages, Gov. Paul LePage signed a "limited emergency declaration" so power crews from other states and Canada can help the state prepare for Sandy. The declaration also extends the hours that power company crews can drive.
Gov. Martin O'Malley said officials in Maryland prepared for the worst.
"This is going to be a long night," he said late Monday. "We're only now just kind of beginning the rough part of this storm. These next 12 hours will likely be the most intense."
Public schools in Baltimore, Montgomery and Prince George's County were closed Monday. Baltimore Mayor Stephanie Rawlings-Blake announced mandatory travel restrictions for city roadways, starting at 6 p.m. Monday.
In the coastal city of Annapolis, city crews distributed sandbags to residents and businesses to help them prepare for flooding.
Obama declared a state of emergency in Maryland on Sunday.
Gov. Deval Patrick declared a state of emergency for the Bay State.
Hoping to avoid the kind of criticism utilities received after last year's Hurricane Irene and other storms, Patrick said utilities plan to pair tree removal and power restoration crews, rather than having them work separately, so that work can be done more efficiently.
Boston announced that schools were closed Monday, and all public transportation services in the city were suspended. Schools were scheduled to be open Tuesday.
Obama also declared a state of emergency for Massachusetts.
"All in all, we're holding our own," Patrick told reporters Monday afternoon. "I think it's going well, but it's nature, and it can change in a minute."